The verb in the underlined portion of the sentence is in the present tense, while the verb in the first part of the sentence is in the past tense. The two verbs need to match their tenses due to the construction of the sentence. The correct answer choice is " none proved satisfactory."

This sentence does not contain a comma where one is necessary. The phrase "While looking through the company's books" is an example of an introductory phrase, explaining information necessary to the context of the sentence, but outside of the main sentence, grammatically. These types of phrases must be followed by a comma in order to separate them from the rest of the sentence. The correct answer choice is, "the company's books, the accountant found many errors."

The answer choice "include family history, poor diet, and excessive stress" is correct because it contains appropriate parallelism—in this case, a list of three noun phrases.

The original text "include family history, poor diet, and having an excess of stress" and the answer choice "include family history, poor diet, and having an excessive amount of stress" contain faulty parallelism—the last item in the list includes the verb "having" whereas the first two items in the list do not employ verbs. These answers are therefore incorrect.

Answer choices "includes family history, poor diet, and excessive stress" and "tends to include family history, poor diet, and excessive stress" are incorrect because they both use singular predicates for the plural subject, "risk factors for cardiovascular disease."

The sentence describes what the soldier had already done to his own body. The use of "himself" is correct and necessary to show who the action was done to, but the action occurred in the past, meaning the appropriate verb form is "backed." The correct answer choice is "had backed himself."

This sentence misuses the word "it's." It's is a contraction for "it is," but it is clear from the context of the sentence that what is needed here is the possessive form of the word: its. The possessive form of "it" does not include an apostrophe before the s. Furthermore, the form " its' " is not an actual form of "it" - it is not a word - and no comma is necessary in this sentence. The best choice is, "with the introduction of its iPhone."

This problem provides two very clear decision points for you to get started:

1. "they" vs. "it" as the first word of the sentence

2. "that of" vs. "those of" vs. (no possessive) in relation to "the Medieval period"

The key to both of these is recognizing the subject of the sentence which is "global temperatures." Since temperatures is plural, the pronoun that corresponds to them must be "they" and you can eliminate choices "it has only recently eclipsed the Medieval period, during which, scientists theorize, a" and "it has only recently eclipsed that of the Medieval period, during which scientists theorize a".

Then notice that the comparison is between current global temperatures and the temperatures during the Medieval period; you cannot logically compare "temperatures" with the timeframe, so you need to have "those of" (which "they have only recently eclipsed those of the Medieval period, during which scientists theorize that a" and "it has only recently eclipsed that of the Medieval period, during which scientists theorize a" have but "they have only recently eclipsed the Medieval period, during which scientists theorize that a" does not) to properly draw the comparison.

Between "they have only recently eclipsed those of the Medieval period, during which scientists theorize that a" and "they have only recently eclipsed those of the Medieval period, during which, scientists theorize, a", notice that the only difference is commas around "during which." Why is that important? Here you're dealing with a tense/timeline decision. Since "theorize" is present-tense but the Medieval period is clearly in the past (even if you're not a historian, the fixed past tense "sent" outside the underline tells you that those volcanoes were in the past), you cannot have "scientists theorize" as part of the phrase "during which." The scientists currently theorize that volcanoes caused the global warming, so you need to separate that subject-verb from the modifier "during (the Medieval period)." This means that answer choice "they have only recently eclipsed those of the Medieval period, during which, scientists theorize, a" is correct.

The sentence is written in such a way to make it seem like the "project" was "making plenty of mistakes." The sentence needs to be reworded and restructured to show that it was "the young associate" who was "making plenty of mistakes." The correct answer choice is the only answer choice that makes this clear, "The project was taken away from the young associate because he was making plenty of mistakes."

An illusion is a hallucination, an image that isn’t really there. An allusion is a reference or citation, especially to/from another text. Also, there is a split infinitive; the adverb “tactfully” must be moved elsewhere in the sentence so the verb “to reference” is kept together.

The phrase "Due to the company's budget problems" is an example of an introductory phrase, explaining information necessary to the context of the sentence, but outside of the main sentence, grammatically. These types of phrases must be followed by a comma in order to separate them from the rest of the sentence. The correct answer choice is "Due to the company's budget problems, management started a round of layoffs. "

This sentence is structured as an independent clause about a priority and then a clarification of what that priority is.

The only appropriate punctuation here is a colon, which will provide that correct structural division and allow the second part of the sentence ("studying physics before her final exam the next morning") to act as an explanation of the noun "priority."

INCORRECT EXPLANATIONS:

A semicolon connects two separate independent clauses, so that is incorrect.

Janine's priority is "studying," which is a gerund, so the past tense "studied" is incorrect.

The option that uses a comma is incorrect because the second clause is dependent and is lacking a subject.

The option that uses a colon unnecessarily includes the connector "and that was." These superfluous words cloud the sentence's meaning and make the sentence grammatically incorrect.