Spanish 2 Quiz: Correcting Preterite Errors
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Correcting Preterite ErrorsQuestion 1 of 10

A student writes: "La semana pasada, nosotros fuimos al cine y vimos una película excelente."

A teacher marks this sentence as containing a preterite error. Which of the following best explains whether the teacher is justified, and why?

The teacher is justified because "fuimos" is the nosotros imperfect form of ir; the correct nosotros preterite of ir is "íbamos," which should be used to express the completed trip to the cinema.
The teacher is justified because "vimos" is incorrectly formed; ver is a regular -ER verb in the preterite and the nosotros form should be "vemos," following the standard -ER nosotros preterite ending -emos.
The teacher is not justified; both "fuimos" and "vimos" are correctly formed irregular preterite forms — "fuimos" is the nosotros preterite of ir (sharing its paradigm with ser), and "vimos" is the nosotros preterite of ver — and the sentence is grammatically correct.
The teacher is justified because both verbs lack accent marks; standard preterite nosotros forms require a written accent on the final syllable to distinguish them from present-tense forms, so the correct forms are "fuímos" and "vímos."
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Spanish 2 Quiz

Spanish 2 Quiz: Correcting Preterite Errors

Practice Correcting Preterite Errors in Spanish 2 with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Correcting Preterite Errors, giving you a quick way to practice the rules, question types, and explanations that matter most for Spanish 2.

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.

All questions

Question 1

A student writes: "La semana pasada, nosotros fuimos al cine y vimos una película excelente."

A teacher marks this sentence as containing a preterite error. Which of the following best explains whether the teacher is justified, and why?

  1. The teacher is justified because "fuimos" is the nosotros imperfect form of ir; the correct nosotros preterite of ir is "íbamos," which should be used to express the completed trip to the cinema.
  2. The teacher is justified because "vimos" is incorrectly formed; ver is a regular -ER verb in the preterite and the nosotros form should be "vemos," following the standard -ER nosotros preterite ending -emos.
  3. The teacher is not justified; both "fuimos" and "vimos" are correctly formed irregular preterite forms — "fuimos" is the nosotros preterite of ir (sharing its paradigm with ser), and "vimos" is the nosotros preterite of ver — and the sentence is grammatically correct. (correct answer)
  4. The teacher is justified because both verbs lack accent marks; standard preterite nosotros forms require a written accent on the final syllable to distinguish them from present-tense forms, so the correct forms are "fuímos" and "vímos."
Explanation: When you encounter a question about preterite forms, your first instinct should be to verify whether each verb form actually exists and belongs to the correct tense — not just whether the sentence "sounds right." This question tests your knowledge of irregular preterite paradigms, which are among the most commonly confused forms in Spanish 2. Both verbs in the sentence are correct, making C the right answer. Ir and ser share an identical preterite conjugation: fui, fuiste, fue, fuimos, fuisteis, fueron. So "fuimos" is unambiguously the nosotros preterite of ir. Meanwhile, ver is irregular in the preterite — it uses the -ER preterite endings but without the accent marks: vi, viste, vio, vimos, visteis, vieron. "Vimos" is therefore correctly formed. The sentence describes a completed, specific past event ("last week"), which is precisely the context where the preterite belongs. The teacher is not justified. Answer A contains a critical reversal: "íbamos" is the nosotros imperfect of ir, not the preterite. Swapping these two tenses is the opposite of what the sentence needs. Answer B misidentifies "vemos" as a preterite form — it's actually the present tense of ver. The claim that regular -ER nosotros preterite ends in -emos is simply false; it ends in -imos (e.g., "comimos"). Answer D invents a rule that doesn't exist. Nosotros preterite forms like "fuimos" and "vimos" carry no written accent — unlike first- and third-person singular forms (e.g., "hablé," "habló"). Your study tip: memorize the ir/ser shared preterite paradigm and ver's irregular preterite as a set — these three verbs appear constantly on exams precisely because students confuse their forms across tenses.

Question 2

En una composición, un alumno escribió: "Ayer el cocinero sirvió la sopa caliente, pero los clientes no la pedieron porque ya estaban llenos."

The sentence contains a preterite error involving a stem-changing verb. Which answer correctly identifies the error and provides the accurate correction?

  1. "pedieron" is incorrect because pedir is an -IR stem-changing verb (e→i); in the preterite, the stem change (e→i) applies to the third-person singular and plural forms, so the correct ellos preterite form is pidieron, not "pedieron." (correct answer)
  2. "sirvió" is incorrect; servir is an -IR stem-changing verb (e→i), but in the preterite the stem change only affects yo and él/ella forms, so the correct third-person singular form should be "servió" without the stem change.
  3. "pedieron" is incorrect because -IR verbs whose stems end in -ed must insert a y before the -ieron ending to avoid a vowel cluster, making the correct form "pedyeron" by analogy with verbs like leer.
  4. "pedieron" is incorrect because pedir is irregular in all preterite forms and must use the same root as dar; the correct ellos form is therefore "pideron" without the intervocalic i in the ending.
Explanation: When working with preterite forms of stem-changing verbs in Spanish, the key rule to remember is that only -IR verbs carry their stem change into the preterite — and even then, only in the third-person singular (él/ella) and plural (ellos/ellas) forms. This is exactly what this question tests. The verb pedir (e→i) is an -IR stem-changing verb. In the preterite, the stem change applies to the él form ("pidió") and the ellos form ("pidieron"). The student wrote "pedieron," which incorrectly keeps the original stem vowel e instead of shifting it to i. Answer A correctly identifies this error and supplies the accurate form: pidieron. The reasoning is precise — the e→i shift is required for third-person forms of -IR stem-changers in the preterite. Answer B is a trap because it targets "sirvió," which is actually correct. Servir (e→i) follows the same -IR rule, so "sirvió" is the proper él preterite form. Don't second-guess a form that's already right. Answer C invents a rule that doesn't exist. The y-insertion rule (as in leer → leyeron) applies when a vowel would fall between two other vowels in -ER/-IR verbs whose stems end in a vowel — not simply because a stem ends in "-ed." Pedir doesn't trigger this rule at all. Answer D is entirely fabricated. Pedir doesn't borrow forms from dar, and "pideron" isn't a real conjugation in any context. Study tip: Memorize the -IR stem-changers (e→i and o→u) and flag their él/ellos preterite forms — those are the two slots where the stem shifts. All other preterite forms for these verbs stay regular.

Question 3

En un foro de idiomas, alguien publicó: "Mi hermano se cayó de la bicicleta y se rompió el brazo el año pasado."

A peer reviewer makes two claims about "se cayó": (1) that it is correctly spelled with the accent mark on the ó, and (2) that the y is an error — the verb caer should be conjugated as "se caió" (without the y) in the preterite él/ella form. Which response most accurately evaluates these two claims?

  1. The reviewer is correct on both counts; reflexive preterite él/ella forms require a written accent, and the y in "cayó" is an error — the correct form is "se caió" since reflexive verbs do not undergo the vowel-to-y spelling change.
  2. The reviewer is correct that the accent mark on the ó is required, but wrong about removing the y; however, since the original "se cayó" already carries the accent and the y, both of the reviewer's claims misread the original sentence.
  3. The reviewer is wrong on both counts; "se cayó" should be written "se cáyo" with the accent on the a, since the stressed syllable in third-person preterite forms of stem-vowel verbs shifts to the penultimate position, and no y is needed.
  4. The reviewer is correct on claim (1) but wrong on claim (2); the original "se cayó" is correctly spelled because caer has a vowel-ending stem, which requires the i of the preterite ending -ió to become y, producing "cayó" — so the original sentence contains no error in this verb. (correct answer)
Explanation: When you see a question about Spanish preterite spelling, think about two separate rules: written accent marks on preterite endings, and spelling-change verbs whose stems end in a vowel. The verb caer has a stem ending in the vowel a (ca-). In the preterite, the third-person singular ending is -ió. However, Spanish does not allow an unstressed i to sit between two vowels — it must become y. So ca + ió → cayó. The accent mark on the ó is then required to signal that the stress falls on that final syllable, just as it does for all regular preterite él/ella forms (habló, comió). This means the original "se cayó" is perfectly correct — the y is mandatory, not an error, and the accent is properly placed. That confirms D as the right answer: the reviewer is correct about the accent mark but wrong to call the y an error. A is wrong because it accepts the reviewer's false claim that the y is an error. Reflexive or not, caer still undergoes the vowel-to-y spelling change — reflexivity is irrelevant to this rule. B is wrong in a subtle way: it correctly identifies the accent as valid and the y as necessary, but then claims both of the reviewer's claims misread the sentence. In fact, claim (1) — that the accent is required — is accurate, so the reviewer is not wrong on both points. C is entirely wrong; the accent in preterite él/ella forms never shifts to the penultimate syllable. Cayó with the accent on the final ó is standard. As a study tip, memorize that verbs like caer, leer, and oír — whose stems end in a vowel — change the i to y in the preterite third-person forms: cayó, leyó, oyó.

Question 4

Carlos le mandó un mensaje a su profesor: "Ayer no asistí a clase porque me dolia el estómago todo el día."

The message contains a verb form error. Considering both tense choice and spelling, which answer correctly identifies and fixes the problem?

  1. "asistí" is incorrect; because the absence lasted "todo el día," a duration is implied, so the correct form should be "asistía" to reflect an ongoing past condition.
  2. "dolia" is a spelling error; the correct yo preterite form of doler is "dolí," which properly expresses the completed stomachache using the standard -ER preterite ending.
  3. "dolia" is incorrectly formed; the phrase "todo el día" signals an ongoing background condition in the past — a classic trigger for the imperfect — so the correct form is dolía (with the required accent mark on the i), not a preterite form. (correct answer)
  4. "asistí" is incorrect because attendance verbs in formal written Spanish require the present perfect construction; the correct form is "he asistido" using the auxiliary haber.
Explanation: When analyzing past-tense errors in Spanish, always ask yourself two questions: Which verb is actually wrong? and Does the context call for a completed action (preterite) or an ongoing background condition (imperfect)? Here, the verb to scrutinize is "dolia." The phrase "todo el día" is a classic imperfect trigger — it signals a condition that stretched continuously throughout the day, serving as background context for why Carlos missed class. The imperfect of doler in the third person singular is dolía, with a required written accent mark on the í. That accent isn't optional; without it, the word is misspelled and the vowels blend incorrectly. So "dolia" fails on two levels: wrong register (imperfect vs. what sounds like a botched preterite) and missing the accent. C correctly identifies both the tense logic and the orthographic fix. A is wrong because "asistí" is actually correct — the absence was a single, completed event ("yesterday I didn't attend"), which is exactly what the preterite expresses. Changing it to "asistía" would imply a habitual or ongoing pattern of not attending, which distorts the meaning. B misidentifies the problem by treating "dolia" as a failed preterite attempt and suggesting "dolí." But doler is a third-person verb here (the stomach hurts him), not first-person, so "dolí" makes no grammatical sense in this sentence regardless of tense. D invents a grammar rule that doesn't exist — Spanish does not require haber + participle for formal written absence statements. Study tip: Memorize duration/description words like todo el día, siempre, and mientras as automatic imperfect signals, and always double-check accent marks on imperfect -ER/-IR forms (comía, dolía, vivía).

Question 5

Una alumna escribió en un examen: "Cuando era niña, mi familia hizo un viaje a México cada verano."

The sentence contains an error involving a verb that is irregular in the preterite. Which answer correctly identifies and corrects the mistake in context?

  1. "hizo" is incorrect because it is the irregular preterite form of hacer for él/ella, but the subject is mi familia acting habitually; the correct form is the imperfect hacía to express a repeated past action. (correct answer)
  2. "hizo" is incorrect because irregular preterite forms like hizo can only be used with animate, human subjects; since familia is a collective noun, the correct form is the regular preterite "hació."
  3. "hizo" is incorrect in this sentence because the presence of "cuando era niña" requires all subsequent verbs to appear in the imperfect; therefore "hizo" must be changed to "hacía" regardless of whether the action was habitual or not.
  4. "hizo" is the correct preterite form of hacer for third-person singular, and no error exists; the sentence is grammatically acceptable because "cada verano" can modify a preterite verb when the timeframe is specific.
Explanation: When you see a verb in a Spanish passage alongside time expressions like "cada verano" (every summer) or "cuando era niña" (when I was a girl), your first instinct should be to ask: is this action completed once, or was it a repeated habit? That distinction drives the preterite vs. imperfect decision. Here, "mi familia hizo un viaje a México cada verano" describes something that happened repeatedly over time — a childhood habit. That calls for the imperfect, which expresses ongoing or habitual past actions. The correct form is hacía. Answer A captures this perfectly: hizo is indeed the legitimate irregular preterite of hacer for él/ella/usted, and mi familia is grammatically third-person singular — so the conjugation itself isn't the problem. The problem is the tense choice given the habitual context signaled by "cada verano." Answer B is a trap built on a fake grammar rule. There is no restriction in Spanish limiting irregular preterite forms to animate or human subjects, and "hació" doesn't even exist — hacer is irregular in the preterite precisely because it doesn't follow regular patterns. Answer C overstates the rule about "cuando era niña." While that clause does use the imperfect, it doesn't automatically force every subsequent verb into the imperfect. Each verb must be evaluated independently based on its own meaning and context. Answer D incorrectly claims the sentence is fine as written, ignoring how "cada verano" signals repetition, which is incompatible with the preterite regardless of whether the timeframe seems specific. Study tip: Memorize these imperfect trigger words — siempre, cada, todos los días, de niño/a, frecuentemente — they almost always signal habitual past action, making the imperfect the right call.

Question 6

Un estudiante escribió: "El sábado pasado, nosotros volvimos a casa tarde y dormieron ocho horas."

The sentence above contains one preterite conjugation error. Which answer correctly identifies the error and provides the proper correction?

  1. "volvimos" is incorrect because -ER verbs use -imos only in the present tense for nosotros; the preterite nosotros form should be "volvemos" to reflect completed action.
  2. "dormieron" is incorrect because the subject is nosotros, not ellos/ellas; the correct preterite nosotros form of dormir is "dormimos," not the third-person plural form used here. (correct answer)
  3. "dormieron" is incorrect because dormir is a stem-changing verb and the yo stem change must be applied to all forms; the correct nosotros preterite form is therefore "durmimos."
  4. "volvimos" is incorrect because the preterite nosotros form of -ER verbs requires an accent mark; it should be written "volvímos" to distinguish it from the present tense form.
Explanation: When you spot a preterite conjugation error, your first move should be to match the verb ending to its subject. In this sentence, the subject is nosotros throughout — both "volvimos" and the second verb need to reflect that. "Volvimos" is actually correct: volver is a regular -ER verb, and the nosotros preterite ending for -ER/-IR verbs is -imos, giving you volvimos. The problem is the second verb. Dormir with a nosotros subject requires the nosotros preterite ending -imos as well, producing dormimos. Instead, the sentence uses "dormieron," which is the ellos/ellas/ustedes preterite form — a clear subject-verb mismatch. That makes B the correct answer. Answer A is wrong on two counts: volvimos is perfectly correct, and the claim that -ER verbs use -imos only in the present is false — the nosotros preterite for -ER/-IR verbs is also -imos (which is exactly why present and preterite look identical for nosotros in these verbs). Answer C contains a tempting misconception: while dormir does have a stem change (o→u) in the preterite, that change only applies to the third-person forms (durmió, durmieron), not to nosotros. So "durmimos" is incorrect — the right form is "dormimos." Answer D is simply false; volvimos requires no accent mark, and there is no rule requiring one to distinguish preterite nosotros from present tense. As a study tip, remember: for nosotros preterite, stem-changing -IR verbs like dormir, servir, and pedir do not take the stem change — that's an ellos/ella-only rule in the preterite.

Question 7

Marta escribió en su diario: "Ayer yo fui al mercado y comprí muchas verduras frescas."

Marta's diary entry contains a preterite error. Which of the following best identifies and corrects the error?

  1. "fui" is incorrect because it is irregular; it should be replaced with "fuí" (with an accent mark) to follow standard preterite orthography for yo forms.
  2. "comprí" is incorrect because -AR verbs do not take an accented -í in the yo preterite; the correct form is "compré" following the standard -AR preterite conjugation pattern. (correct answer)
  3. "comprí" is incorrect because it uses the -IR verb ending instead of the correct -AR ending; however, the proper correction is "compró" since the subject is third person.
  4. "fui" is incorrect because it is the imperfect form of ir; it should be replaced with "iba" to accurately express a completed past action in context.
Explanation: When conjugating verbs in the Spanish preterite tense, the ending you use depends entirely on whether the verb is an -AR, -ER, or -IR verb. This question tests whether you can spot a mismatch between a verb's infinitive class and its preterite ending. Look at "compré" — this comes from comprar, an -AR verb. The standard yo preterite endings are -é for -AR verbs and -í for -ER/-IR verbs. Marta wrote "comprí," which incorrectly applies the -ER/-IR ending to an -AR verb. The correct form is compré, making B the right answer. As for the distractors: A is a trap for students who second-guess irregular verbs. Fui is indeed the correct yo preterite of ir — it's irregular, but it's not wrong. Adding an accent (fuí) is actually incorrect; monosyllabic preterite forms like fui do not carry accent marks in modern Spanish orthography. C correctly identifies "comprí" as the error but then wrongly "corrects" it to compró, which is the third-person singular form — Marta is writing about herself (yo), so this fix introduces a new subject agreement error. D confuses fui with the imperfect, but iba is the imperfect of ir, used for ongoing or habitual past actions. Since Marta is describing a single completed trip to the market, the preterite fui is exactly right. A reliable study tip: memorize the two yo preterite ending sets — -AR → -é and -ER/-IR → -í — and always check that a verb's ending matches its infinitive class before moving on.

Question 8

A student wrote the following sentence: "Anoche ellos leyeron el artículo, pero yo no lei nada."

There is a preterite spelling error in the sentence. Which answer correctly identifies the error and explains the orthographic rule that applies?

  1. "leyeron" is incorrect; when the preterite stem ends in a vowel, the ellos form should use -ieron without the y, making the correct form "leieron" to avoid the irregular spelling.
  2. "lei" is incorrect because it is missing the required written accent mark; the correct yo preterite form is leí, since the accent mark is needed to break the diphthong and indicate that the i is a separate stressed syllable, not part of a diphthong with the preceding e. (correct answer)
  3. "lei" is incorrect because -ER verbs whose stems end in a vowel must insert a y in the yo preterite form to avoid a vowel cluster; the correct spelling is therefore "leyi."
  4. "lei" is incorrect because the yo preterite of -ER verbs ending in a vowel takes the ending -í only with an additional written accent on the stem vowel; the correct form is therefore "léi" with the accent on the first syllable.
Explanation: When you see preterite forms of verbs like leer, creer, or oír — verbs whose stems end in a vowel — you need to think about two distinct spelling rules: the y insertion rule for third-person forms, and the written accent rule for the yo form. The yo preterite ending for regular -ER/-IR verbs is -í. When the verb stem ends in a vowel (le- from leer), that í sits right next to another vowel. Spanish orthography requires a written accent mark on the í to signal that it forms its own separate syllable rather than blending into a diphthong with the e. Without the accent, lei looks like a diphthong [ley], which misrepresents the pronunciation. The correct form is leí — two distinct syllables: le-í. Answer B correctly identifies this rule and is the right answer. Answer A is backwards: leyeron is actually correct. When the stem ends in a vowel, Spanish inserts y between the two vowels in the third-person forms (leyó, leyeron) to avoid an awkward vowel cluster. Removing the y to make "leieron" would be the real error. Answer C invents a rule that doesn't exist. The y insertion applies only to third-person forms (él/ella and ellos/ellas), never to the yo form. "Leyi" is not a real conjugation. Answer D places the accent on the stem vowel (é), which is incorrect. The accent belongs on the ending í — not the stem — because it's the í that needs to be separated from the adjacent vowel. Study tip: For vowel-stem verbs in the preterite, memorize the pattern leí, leíste, leyó, leímos, leísteis, leyeron — accent on í for most forms, y for third-person only.

Question 9

Un estudiante completó la siguiente oración: "Mis padres me dieron un regalo especial y yo les di las gracias inmediatamente."

A classmate claims there is a preterite error in this sentence. Which of the following best evaluates this claim?

  1. The classmate is correct: "dieron" should be "daron" because dar is a regular -AR verb in the preterite, and the ellos form of regular -AR verbs takes the ending -aron, not the -ieron ending borrowed from -ER/-IR verbs.
  2. The classmate is correct: "di" should be "dé" because the yo preterite of dar follows the -AR pattern and should end in -é, just as comprar becomes compré and hablar becomes hablé.
  3. The classmate is correct: both "dieron" and "di" lack written accent marks; the correct forms are "diéron" and "dí" because all irregular preterite forms require a written accent to signal their irregular status.
  4. The classmate is incorrect: both "dieron" and "di" are the standard, accepted preterite forms of dar; the verb dar is irregular in the preterite and takes -ER/-IR endings without accent marks, making the sentence entirely correct as written. (correct answer)
Explanation: When you see a question testing preterite conjugations of dar, the key concept to recall is that dar is one of Spanish's most important irregular verbs — and its irregularity is precisely that it behaves like an -ER/-IR verb even though it ends in -AR. The verb dar takes the same preterite endings as -ER/-IR verbs: di, diste, dio, dimos, disteis, dieron. Crucially, because these forms are only one or two letters long (like di and dio), Spanish orthographic rules do not require accent marks — there is no ambiguity to resolve. The sentence "Mis padres me dieron un regalo especial y yo les di las gracias" is completely correct as written, confirming that D is the right answer. The classmate's claim of an error is simply wrong. Choice A contains a tempting-sounding logic: since dar ends in -AR, why not use -aron? The flaw is that dar is explicitly irregular in the preterite and does not follow the regular -AR pattern at all. Choice B makes the same category error, assuming dar behaves like comprar or hablar and that the yo form should be dé. This is incorrect — dé is actually the present subjunctive of dar, not a preterite form. Choice C invents a rule that doesn't exist: irregular preterites do not automatically require accent marks. In fact, di and dio specifically drop accents that older Spanish once used, because modern rules make them unnecessary. Your study tip: memorize dar alongside ver — both are short -AR/-ER verbs that share identical irregular preterite conjugations (di/vi, dio/vio, etc.) with no accent marks required.

Question 10

Two students are debating the following sentence: "Ayer tú tuvistes mucha suerte en el examen."

Student A says the error is that "tuvistes" should be "tuviste" because the tú preterite form never takes a final -s. Student B says the error is different: "tuviste" is also wrong because tener is not truly irregular — it should be "teniste." Which evaluation is accurate?

  1. Student B is correct; tener follows a predictable pattern in the preterite for -ER verbs, making the tú form "teniste," and Student A is wrong to defend "tuviste" as correct since that stem does not appear in standard conjugation tables.
  2. Both students are partially correct; the tú preterite form should be "teniste" (regular -ER ending) written without a final -s, combining both students' observations into the fully corrected form.
  3. Student A is correct and Student B is incorrect; tener is genuinely irregular in the preterite with the stem tuv-, making "tuviste" the correct tú preterite form, while "tuvistes" is wrong because preterite tú forms in Spanish never end in -s. (correct answer)
  4. Neither student is correct; the sentence has no error because "tuvistes" is an accepted regional variant of the tú preterite in several Spanish-speaking countries and is therefore grammatically valid in standard written Spanish.
Explanation: When tackling preterite questions, you need to evaluate two things simultaneously: whether the verb stem is correct and whether the ending is correct. Both layers matter here. Tener is a stem-changing irregular verb in the preterite — it doesn't follow the standard -ER pattern at all. Instead, it uses the stem tuv-, giving you: tuve, tuviste, tuvo, tuvimos, tuvisteis, tuvieron. This stem shift is simply memorized; there's no rule that derives it from the infinitive. So "tuviste" is the legitimate, standard tú form. Now, the sentence uses "tuvistes" — that extra -s at the end is a hypercorrection. Because tú takes an -s in the present tense (tienes, comes, vives), some speakers mistakenly add -s to preterite tú forms. Standard Spanish never does this: tú preterite endings are -é / -aste / -iste, never with a trailing -s. Student A correctly identifies this error and correctly defends "tuviste." That makes C the right answer. A is wrong because it accepts Student B's false claim that tener is regular in the preterite. "Teniste" is not a valid form — tener has an irregular stem (tuv-) that must be memorized. B combines both students' errors into one hybrid non-answer: "teniste" without the -s is still wrong because the stem itself is incorrect. D is a trap — while "tuvistes" occasionally appears in informal regional speech, it is not accepted in standard written Spanish, so calling the original sentence error-free is inaccurate. Your study tip: keep a dedicated list of preterite irregulars with stem changes (tener→tuv-, estar→estuv-, poder→pud-, etc.) and drill them separately from regular verbs — they won't follow any pattern you can predict from the infinitive.