4th Grade Writing Quiz: Comma In Compound Sentences

What this quiz covers

This quiz focuses on Comma In Compound Sentences, giving you a quick way to practice the rules, question types, and explanations that matter most for 4th Grade Writing.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Marcus wanted the blue notebook but, Sofia chose it first.
2. Marcus wanted the blue notebook, but Sofia chose it first. (correct answer)
3. Marcus wanted the blue notebook but Sofia chose it first.
4. Marcus wanted the blue notebook, Sofia chose it first.

Explanation: This question tests CCSS.L.4.2.c: using a comma before a coordinating conjunction in a compound sentence. Students must recognize compound sentences (two independent clauses joined by and/but/or/so) and place commas correctly. A compound sentence has two independent clauses (complete sentences) joined by a coordinating conjunction (FANBOYS: For, And, Nor, But, Or, Yet, So - focus on and, but, or, so for 4th grade). The rule is: use a comma BEFORE the coordinating conjunction when joining two independent clauses. The conjunction "but" shows contrast between the two clauses. In this sentence, there are two independent clauses. The first independent clause is "Marcus wanted the blue notebook" and the second independent clause is "Sofia chose it first" joined by "but". Since both parts can stand alone as complete sentences, this is a compound sentence that needs a comma before the conjunction. Choice B is correct because it places the comma before the coordinating conjunction "but" in the compound sentence. The pattern is: Independent clause (Marcus wanted the blue notebook) , but Independent clause (Sofia chose it first). Both parts can stand alone as sentences, so comma is needed. Choice A represents comma in wrong position error, which occurs when students put comma after conjunction instead of before. The comma must come BEFORE the conjunction "but", not after. To help students: Remember the comma comes BEFORE the conjunction, creating a pause before the connecting word. Independence test: "Marcus wanted the blue notebook" ✓ complete, "Sofia chose it first" ✓ complete, so comma before "but". Watch for: comma after conjunction ("but,"), no comma (Choice C), or comma splice without conjunction (Choice D). Teaching strategy: Have students read aloud - the natural pause comes before "but", not after. Create practice sentences showing contrast with "but" to reinforce the pattern of comma placement.

Question 2

1. Jamal finished his homework and, he played basketball afterward.
2. Jamal finished his homework, and he played basketball afterward. (correct answer)
3. Jamal finished his homework and he played basketball afterward.
4. Jamal, finished his homework and he played basketball afterward.

Explanation: A compound sentence needs a comma before the conjunction that joins two complete sentences, so the comma belongs before "and." Answer A is wrong because the comma comes after "and" instead of before it. Answer C is wrong because it is missing the comma completely. Answer D is wrong because the comma breaks up the first complete sentence instead of joining the two parts.

Question 3

1. Emma forgot her notebook so she borrowed paper from a friend.
2. Emma forgot her notebook, so she borrowed paper from a friend. (correct answer)
3. Emma forgot her notebook, and borrowed paper, from a friend.
4. Emma forgot her notebook, she borrowed paper from a friend.

Explanation: The correct sentence puts a comma before the joining word "so" because it connects two complete sentences: "Emma forgot her notebook" and "she borrowed paper from a friend." One sentence leaves out the comma completely, so nothing signals where the two parts join. Another adds a comma after "and" and a second comma before "from a friend"; both commas break up one single idea instead of joining two complete sentences, so they are placed wrongly. The last sentence uses a comma but drops the joining word, which glues two complete sentences together and creates a run-on. Only the sentence with a comma right before "so" joins the two complete parts the correct way.

Question 4

1. Maya wanted to play outside but it started to rain after school.
2. Maya wanted to play outside, but it started to rain after school. (correct answer)
3. Maya wanted to play outside but, it started to rain after school.
4. Maya wanted to play outside, it started to rain after school.

Explanation: This question tests CCSS.L.4.2.c: using a comma before a coordinating conjunction in a compound sentence. Students must recognize compound sentences (two independent clauses joined by and/but/or/so) and place commas correctly. A compound sentence has two independent clauses (complete sentences) joined by a coordinating conjunction (FANBOYS: For, And, Nor, But, Or, Yet, So - focus on and, but, or, so for 4th grade). The rule is: use a comma BEFORE the coordinating conjunction when joining two independent clauses. Pattern: [Independent clause] , [conjunction] [independent clause]. In this sentence, there are two independent clauses. The first independent clause is 'Maya wanted to play outside' and the second independent clause is 'it started to rain after school' joined by 'but'. Since both parts can stand alone as complete sentences, this is a compound sentence that needs a comma before the conjunction. Choice B is correct because it places the comma before the coordinating conjunction 'but' in the compound sentence. The pattern is: Independent clause (Maya wanted to play outside) , but Independent clause (it started to rain after school). Both parts can stand alone as sentences, so comma is needed. Choice A represents missing comma in compound sentence, which occurs when students forget to add comma before conjunction in compound sentences. Without the comma, the compound sentence is incorrectly punctuated. To help students: Teach the 'independence test' - cover up one side of the conjunction. If the words before the conjunction can stand alone as a complete sentence AND the words after can stand alone as a complete sentence, it's compound and needs a comma before the conjunction. Watch for: forgetting comma in compound sentences, putting comma after conjunction instead of before (Choice C), or creating a run-on sentence without the conjunction (Choice D).

Question 5

1. Yuki wanted the blue marker, but Chen wanted it too. (correct answer)
2. Yuki wanted the blue marker but Chen wanted it too.
3. Yuki wanted the blue marker, but, Chen wanted it too.
4. Yuki wanted the blue marker but, Chen wanted it too.

Explanation: A compound sentence joining two complete ideas with but needs a comma right before but. The first choice places the comma correctly, right before but. The second choice leaves out the comma entirely. The third choice adds an extra, unneeded comma right after but. The fourth choice puts the comma after but instead of before it, which is the wrong spot.

Question 6

1. Amir fed the fish, so the tank stayed clean. (correct answer)
2. Amir fed the fish so, the tank stayed clean.
3. Amir, fed the fish so the tank stayed clean.
4. Amir fed the fish so the tank, stayed clean.

Explanation: A comma belongs right before so when it joins two complete sentences, so the comma goes after fish in the correct choice. The second choice places the comma after so instead of before it, which is incorrect. The third choice places a comma right after the subject Amir, splitting words that belong together. The fourth choice places the comma in the middle of the second idea, which is also the wrong spot.

Question 7

1. Chen was tired, so he went to bed early last night. (correct answer)
2. Chen was tired so, he went to bed early last night.
3. Chen was tired so he went to bed early last night.
4. Chen was tired, he went to bed early last night.

Explanation: This question tests CCSS.L.4.2.c: using a comma before a coordinating conjunction in a compound sentence. Students must recognize compound sentences (two independent clauses joined by and/but/or/so) and place commas correctly. A compound sentence has two independent clauses (complete sentences) joined by a coordinating conjunction (FANBOYS: For, And, Nor, But, Or, Yet, So - focus on and, but, or, so for 4th grade). The rule is: use a comma BEFORE the coordinating conjunction when joining two independent clauses. In this sentence, there are two independent clauses. The first independent clause is 'Chen was tired' and the second independent clause is 'he went to bed early last night' joined by 'so'. Since both parts can stand alone as complete sentences, this is a compound sentence that needs a comma before the conjunction. Choice A is correct because it places the comma before the coordinating conjunction 'so' in the compound sentence. The pattern is: Independent clause (Chen was tired) , so Independent clause (he went to bed early last night). Both parts can stand alone as sentences, so comma is needed. Choice C represents missing comma in compound sentence, which occurs when students forget to add comma before conjunction in compound sentences. Without the comma, the compound sentence is incorrectly punctuated. To help students: Practice identifying: (1) Find the conjunction (and, but, or, so). (2) Test both sides - can each stand alone? (3) If YES to both → compound → USE COMMA before conjunction. Watch for: forgetting comma in compound sentences (Choice C), putting comma after conjunction instead of before (Choice B), or creating a run-on sentence without the conjunction (Choice D).

Question 8

1. Chen was tired, so he went to bed early last night. (correct answer)
2. Chen was tired so, he went to bed early last night.
3. Chen was tired so he went to bed early last night.
4. Chen was tired, so, he went to bed early last night.

Explanation: A compound sentence joins two complete sentences with a joining word like so. Each part must be able to stand alone: "Chen was tired" and "he went to bed early last night" are both complete. The rule is to put the comma BEFORE the joining word. That is why "Chen was tired, so he went to bed early last night" is correct. The choice that puts the comma AFTER so, "Chen was tired so, he went to bed early last night," breaks the rule because the comma should come before the joining word, not after it. The choice with no comma at all, "Chen was tired so he went to bed early last night," forgets the comma that a compound sentence needs before so. The choice with two commas, "Chen was tired, so, he went to bed early last night," adds an extra comma after so; you only need one comma, and it goes before the joining word. Remember: find the joining word (and, but, or, so), check that both sides are complete sentences, then place one comma right before that word.

Question 9

1. Maya wanted to play outside but it started to rain after school.
2. Maya wanted to play outside, but it started to rain after school. (correct answer)
3. Maya wanted to play outside but, it started to rain after school.
4. Maya wanted to play outside, but it started, to rain after school.

Explanation: A compound sentence joins two complete sentences with a joining word like "but." Here the two complete parts are "Maya wanted to play outside" and "it started to rain after school." The rule is to put a comma right BEFORE the joining word. The correct choice does this: it places the comma just before "but," so the sentence is punctuated correctly. The choice with no comma at all forgets the comma that a compound sentence needs before "but." One choice puts the comma AFTER "but" instead of before it, which is the wrong spot for the joining word. The last choice does start with the right comma before "but," but then adds an extra comma after "started" that breaks up the second part for no reason. Only one choice puts a single comma in exactly the right place—right before "but."

Question 10

1. Sofia forgot her folder so, she borrowed paper.
2. Sofia forgot her folder, so she borrowed paper. (correct answer)
3. Sofia forgot, her folder so she borrowed paper.
4. Sofia forgot her folder so she borrowed, paper.

Explanation: This is a compound sentence: two complete thoughts, 'Sofia forgot her folder' and 'she borrowed paper,' joined by the word 'so.' The rule is to put the comma right before the joining word. The correct choice, 'Sofia forgot her folder, so she borrowed paper,' does exactly that. The choice 'Sofia forgot her folder so, she borrowed paper' puts the comma after 'so' instead of before it, which is the wrong spot. The choice 'Sofia forgot, her folder so she borrowed paper' drops the comma in the middle of the first thought, splitting words that belong together. The choice 'Sofia forgot her folder so she borrowed, paper' puts the comma between 'borrowed' and 'paper,' breaking up the second thought instead of marking where the two thoughts join. To check yourself, find the joining word (and, but, or, so), make sure a complete sentence sits on each side, then place the comma just before that joining word.

Question 11

1. Marcus forgot his library book, so he returned it the next day. (correct answer)
2. Marcus forgot his library book so, he returned it the next day.
3. Marcus forgot his library book so he returned it the next day.
4. Marcus forgot his library book, so returned it the next day.

Explanation: This question tests CCSS.L.4.2.c: using a comma before a coordinating conjunction in a compound sentence. Students must recognize compound sentences (two independent clauses joined by and/but/or/so) and place commas correctly. A compound sentence has two independent clauses (complete sentences) joined by a coordinating conjunction (FANBOYS: For, And, Nor, But, Or, Yet, So - focus on and, but, or, so for 4th grade). The rule is: use a comma BEFORE the coordinating conjunction when joining two independent clauses. Pattern: [Independent clause] , [conjunction] [independent clause]. Example: 'I love reading, and my sister loves math.' Both parts can stand alone as sentences ('I love reading' / 'my sister loves math'), so comma is needed before 'and.' DO NOT use comma in simple sentences with compound parts: 'I ran and jumped' (one subject, two verbs - no comma needed). In this sentence, there are two independent clauses: 'Marcus forgot his library book' and 'he returned it the next day' joined by 'so.' Since both parts can stand alone as complete sentences, this is a compound sentence that needs a comma before the conjunction. Choice A is correct because it places the comma before the coordinating conjunction 'so' in the compound sentence. The pattern is: Independent clause (Marcus forgot his library book) , so Independent clause (he returned it the next day). Both parts can stand alone as sentences, so comma is needed. Choice D represents adding comma in simple sentence, which occurs when students add comma in simple sentences with compound predicates thinking all sentences with 'so' need commas. Adding comma before 'so' in 'Marcus forgot his library book, so returned it the next day' is wrong because there's one subject - this is a simple sentence with compound predicate, not a compound sentence. To help students: Teach the 'independence test' - cover up one side of the conjunction. If the words before the conjunction can stand alone as a complete sentence AND the words after can stand alone as a complete sentence, it's compound and needs a comma before the conjunction. Practice identifying: (1) Find the conjunction (and, but, or, so). (2) Test both sides - can each stand alone? (3) If YES to both → compound → USE COMMA. If NO → simple sentence → NO COMMA. Common example: 'I ran home and ate dinner' - Test: 'I ran home' ✓ complete, but 'ate dinner' ✗ not complete (no subject), so this is simple sentence with compound predicate (one subject, two verbs) - NO COMMA. 'I ran home, and I ate dinner' - Test: 'I ran home' ✓ complete, 'I ate dinner' ✓ complete, so compound sentence - USE COMMA. Watch for: forgetting comma in compound sentences ('I ran fast and I won the race' needs comma), adding comma in simple sentences with compound parts ('I ran, and jumped' should not have comma - one subject), confusing compound subject/predicate with compound sentence (compound sentence has two complete thoughts, not just two subjects or two verbs), putting comma after conjunction instead of before. Create practice by having students identify independent clauses before adding punctuation.

Question 12

1. Carlos was thirsty so, he drank a glass of water after recess.
2. Carlos was thirsty, so he drank a glass of water after recess. (correct answer)
3. Carlos was thirsty, so drank a glass of water after recess.
4. Carlos was thirsty so he drank a glass of water after recess.

Explanation: This question tests CCSS.L.4.2.c: using a comma before a coordinating conjunction in a compound sentence. Students must recognize compound sentences (two independent clauses joined by and/but/or/so) and place commas correctly. A compound sentence has two independent clauses (complete sentences) joined by a coordinating conjunction (FANBOYS: For, And, Nor, But, Or, Yet, So - focus on and, but, or, so for 4th grade). The rule is: use a comma BEFORE the coordinating conjunction when joining two independent clauses. Pattern: [Independent clause] , [conjunction] [independent clause]. Example: 'I love reading, and my sister loves math.' Both parts can stand alone as sentences ('I love reading' / 'my sister loves math'), so comma is needed before 'and.' DO NOT use comma in simple sentences with compound parts: 'I ran and jumped' (one subject, two verbs - no comma needed). In this sentence, there are two independent clauses: 'Carlos was thirsty' and 'he drank a glass of water after recess' joined by 'so.' Since both parts can stand alone as complete sentences, this is a compound sentence that needs a comma before the conjunction. Choice B is correct because it places the comma before the coordinating conjunction 'so' in the compound sentence. The pattern is: Independent clause (Carlos was thirsty) , so Independent clause (he drank a glass of water after recess). Both parts can stand alone as sentences, so comma is needed. Choice C represents adding comma in simple sentence, which occurs when students add comma in simple sentences with compound predicates thinking all sentences with 'so' need commas. Adding comma before 'so' in 'Carlos was thirsty, so drank a glass of water' is wrong because there's one subject - this is a simple sentence with compound predicate, not a compound sentence. To help students: Teach the 'independence test' - cover up one side of the conjunction. If the words before the conjunction can stand alone as a complete sentence AND the words after can stand alone as a complete sentence, it's compound and needs a comma before the conjunction. Practice identifying: (1) Find the conjunction (and, but, or, so). (2) Test both sides - can each stand alone? (3) If YES to both → compound → USE COMMA. If NO → simple sentence → NO COMMA. Common example: 'I ran home and ate dinner' - Test: 'I ran home' ✓ complete, but 'ate dinner' ✗ not complete (no subject), so this is simple sentence with compound predicate (one subject, two verbs) - NO COMMA. 'I ran home, and I ate dinner' - Test: 'I ran home' ✓ complete, 'I ate dinner' ✓ complete, so compound sentence - USE COMMA. Watch for: forgetting comma in compound sentences ('I ran fast and I won the race' needs comma), adding comma in simple sentences with compound parts ('I ran, and jumped' should not have comma - one subject), confusing compound subject/predicate with compound sentence (compound sentence has two complete thoughts, not just two subjects or two verbs), putting comma after conjunction instead of before. Create practice by having students identify independent clauses before adding punctuation.

Question 13

1. Sofia can draw a poster, or she can write a short report. (correct answer)
2. Sofia can draw a poster or, she can write a short report.
3. Sofia can draw a poster or she can write a short report.
4. Sofia can draw a poster, or write a short report.

Explanation: This question tests CCSS.L.4.2.c: using a comma before a coordinating conjunction in a compound sentence. Students must recognize compound sentences (two independent clauses joined by and/but/or/so) and place commas correctly. A compound sentence has two independent clauses (complete sentences) joined by a coordinating conjunction (FANBOYS: For, And, Nor, But, Or, Yet, So - focus on and, but, or, so for 4th grade). The rule is: use a comma BEFORE the coordinating conjunction when joining two independent clauses. Pattern: [Independent clause] , [conjunction] [independent clause]. Example: 'I love reading, and my sister loves math.' Both parts can stand alone as sentences ('I love reading' / 'my sister loves math'), so comma is needed before 'and.' DO NOT use comma in simple sentences with compound parts: 'I ran and jumped' (one subject, two verbs - no comma needed). In this sentence, there are two independent clauses: 'Sofia can draw a poster' and 'she can write a short report' joined by 'or.' Since both parts can stand alone as complete sentences, this is a compound sentence that needs a comma before the conjunction. Choice A is correct because it places the comma before the coordinating conjunction 'or' in the compound sentence. The pattern is: Independent clause (Sofia can draw a poster) , or Independent clause (she can write a short report). Both parts can stand alone as sentences, so comma is needed. Choice D represents adding comma in simple sentence, which occurs when students add comma in simple sentences with compound predicates thinking all sentences with 'or' need commas. Adding comma before 'or' in 'Sofia can draw a poster, or write a short report' is wrong because there's one subject - this is a simple sentence with compound predicate, not a compound sentence. To help students: Teach the 'independence test' - cover up one side of the conjunction. If the words before the conjunction can stand alone as a complete sentence AND the words after can stand alone as a complete sentence, it's compound and needs a comma before the conjunction. Practice identifying: (1) Find the conjunction (and, but, or, so). (2) Test both sides - can each stand alone? (3) If YES to both → compound → USE COMMA. If NO → simple sentence → NO COMMA. Common example: 'I ran home and ate dinner' - Test: 'I ran home' ✓ complete, but 'ate dinner' ✗ not complete (no subject), so this is simple sentence with compound predicate (one subject, two verbs) - NO COMMA. 'I ran home, and I ate dinner' - Test: 'I ran home' ✓ complete, 'I ate dinner' ✓ complete, so compound sentence - USE COMMA. Watch for: forgetting comma in compound sentences ('I ran fast and I won the race' needs comma), adding comma in simple sentences with compound parts ('I ran, and jumped' should not have comma - one subject), confusing compound subject/predicate with compound sentence (compound sentence has two complete thoughts, not just two subjects or two verbs), putting comma after conjunction instead of before. Create practice by having students identify independent clauses before adding punctuation.

Question 14

1. Amir can sit with us, or he can sit by the window. (correct answer)
2. Amir can sit with us or, he can sit by the window.
3. Amir can sit with us or he can sit by the window.
4. Amir can sit with us, or, he can sit by the window.

Explanation: A compound sentence joins two complete ideas that could each stand alone. Here the ideas are "Amir can sit with us" and "he can sit by the window." When you join them with or, put one comma right before the joining word: "Amir can sit with us, or he can sit by the window." That is the correct choice. The version that places the comma after or is wrong, because the comma should come before the joining word, not after it. The version with no comma at all is wrong too, because two complete ideas joined by or need a comma before or. The version with a comma both before and after or is wrong because it uses one comma too many; you need only the comma before or, not one on each side.

Question 15

1. Marcus practiced the song and, he played it well.
2. Marcus practiced the song, and he played it well. (correct answer)
3. Marcus practiced the song, and, he played it well.
4. Marcus practiced the song and he played it, well.

Explanation: A compound sentence joins two complete sentences with a joining word like and. Here, "Marcus practiced the song" and "he played it well" are both complete on their own, so you put one comma right before the joining word and. That is why "Marcus practiced the song, and he played it well" is correct. The option that puts the comma after and ("the song and, he played it well") is wrong because the comma must come before the joining word, not after it. The option with two commas around and ("the song, and, he played it well") adds an extra comma that does not belong; you only need the one before and. The last option puts a comma before well ("he played it, well"), which breaks up the second complete sentence in a spot where no comma is needed. Remember: find the joining word, check that both sides could stand alone, and place a single comma just before that word.

Question 16

1. Emma forgot her notebook so she borrowed a spare from a friend.
2. Emma forgot her notebook, so she borrowed a spare from a friend. (correct answer)
3. Emma forgot her notebook so, she borrowed a spare from a friend.
4. Emma forgot her notebook, she borrowed a spare so from a friend.

Explanation: A compound sentence joins two complete sentences with a word like 'so,' and the comma goes right before that joining word. Here 'Emma forgot her notebook' and 'she borrowed a spare from a friend' are both complete on their own, so the correct choice puts a comma before 'so': 'Emma forgot her notebook, so she borrowed a spare from a friend.' The choice with no comma leaves the two complete sentences squeezed together with nothing to separate them. The choice with the comma after 'so' breaks up the joining word from the sentence it introduces, which is not where the comma belongs. The last choice adds a comma but drops 'so' into the wrong spot, so 'so' no longer joins the two sentences and the comma just creates a run-on. Only one choice both keeps 'so' as the joining word and places the comma directly in front of it.

Question 17

1. Keisha was thirsty so, she drank water after gym class.
2. Keisha was thirsty, so she drank water after gym class. (correct answer)
3. Keisha was thirsty, she drank water after gym class.
4. Keisha was thirsty so she drank water after gym class.

Explanation: This question tests CCSS.L.4.2.c: using a comma before a coordinating conjunction in a compound sentence. Students must recognize compound sentences (two independent clauses joined by and/but/or/so) and place commas correctly. A compound sentence has two independent clauses (complete sentences) joined by a coordinating conjunction (FANBOYS: For, And, Nor, But, Or, Yet, So - focus on and, but, or, so for 4th grade). The rule is: use a comma BEFORE the coordinating conjunction when joining two independent clauses. Pattern: [Independent clause] , [conjunction] [independent clause]. Example: 'I love reading, and my sister loves math.' Both parts can stand alone as sentences ('I love reading' / 'my sister loves math'), so comma is needed before 'and.' DO NOT use comma in simple sentences with compound parts: 'I ran and jumped' (one subject, two verbs - no comma needed). In this sentence, there are two independent clauses. The first independent clause is 'Keisha was thirsty' and the second independent clause is 'she drank water after gym class' joined by 'so'. Since both parts can stand alone as complete sentences, this is a compound sentence that needs a comma before the conjunction. Choice B is correct because it places the comma before the coordinating conjunction 'so' in the compound sentence. The pattern is: Independent clause (Keisha was thirsty) , so Independent clause (she drank water after gym class). Both parts can stand alone as sentences, so comma is needed. Choice A represents comma in wrong position, which occurs when students put comma after conjunction instead of before. The comma must come BEFORE the conjunction, not after. To help students: Teach the 'independence test' - cover up one side of the conjunction. If the words before the conjunction can stand alone as a complete sentence AND the words after can stand alone as a complete sentence, it's compound and needs a comma before the conjunction. Practice identifying: (1) Find the conjunction (and, but, or, so). (2) Test both sides - can each stand alone? (3) If YES to both → compound → USE COMMA before conjunction. If NO → simple sentence → NO COMMA.

Question 18

1. It was windy so, Keisha held her hat on the walk home.
2. It was windy, so Keisha held her hat on the walk home. (correct answer)
3. It was windy so Keisha held her hat on the walk home.
4. It was windy, so, Keisha held her hat on the walk home.

Explanation: A compound sentence joins two complete sentences with a word like "so." Here both parts stand alone: "It was windy" and "Keisha held her hat on the walk home." The rule is to put the comma BEFORE "so." The correct choice, "It was windy, so Keisha held her hat on the walk home," does exactly that. The choice with the comma after "so" ("It was windy so, Keisha...") puts the comma in the wrong place — it goes before the joining word, not after it. The choice with no comma at all ("It was windy so Keisha...") forgets the comma that a compound sentence needs. The choice with a comma both before and after "so" ("It was windy, so, Keisha...") adds an extra comma; you only need one, and it belongs before "so." Remember: pause with a comma right before "so" when it links two complete sentences.

Question 19

1. Maya wanted to play tag but it started to rain at recess.
2. Maya wanted to play tag, but it started to rain at recess. (correct answer)
3. Maya wanted to play tag but, it started to rain at recess.
4. Maya wanted to play tag, but it started to rain, at recess.

Explanation: In a compound sentence, a comma belongs right before the joining word but. The correct choice puts the comma before but, joining the two complete ideas the right way. One choice leaves out the comma completely, so the two ideas run together with no pause. Another choice puts the comma after but instead of before it, which is the wrong spot. The last choice does place a comma before but, but it also adds an extra comma before at recess, where no comma is needed. Only the choice with a single comma before but is punctuated correctly.

Question 20

1. Chen finished his math, and he started reading. (correct answer)
2. Chen finished his math and, he started reading.
3. Chen, finished his math and he started reading.
4. Chen finished his math and he, started reading.

Explanation: A compound sentence joins two complete sentences with a joining word like "and." Here both parts stand alone: "Chen finished his math" and "he started reading." The rule is to put the comma right BEFORE the joining word "and." That is why placing the comma before "and" is correct. Putting the comma after "and" is wrong because the comma belongs before the joining word, not after it. Putting the comma after "Chen" is wrong because it splits the subject from what he did, and no comma belongs there. Putting the comma after "he" is wrong because it splits the subject "he" from its verb "started," breaking up the second sentence. Only one spot follows the rule: the comma goes before "and."