"There are” is correct because it indicates the existence of more than one thing (e.g., varieties). “Which” is incorrect because it does not follow a comma, nor does it refer to a complement/predicate. 

The use of the singular verb "was" is incorrect with the plural subject "members." Even though the verb is next to the singular group, the verb needs to match the subject. Thus the correct answer choice is "the group were frequently at odds," which is the only choice with the appropriate verb tense.

The subject of the sentence, "Mark and his friend Josh," is plural. Therefore, the sentence must use a verb that agrees with a plural subject. So, "are" needs to be used instead of "is." In choosing between "are a type" and "are a types," the phrase "a types" is grammatically incorrect because "a" is an indefinite article used with singular nouns, and "types" is a plural noun. Plus, you can see that the sentence is discussing one type of person "called introverts"—there is no discussion provided of any other type of person, so using the plural "types" would not make sense in the sentence's context. So, "are a type" is the correct answer.

An apostrophe is necessary to show possession, but the word “director” doesn’t need to be capitalized unless it is the official title or nickname of the person. Since “the quality” is singular, the sentence must read, "Despite positive reviews from movie critics, the quality of the young director’s recent films is rather questionable."

The underlined words, the verb phrase "have become," must be in agreement with the subject of the sentence, which is "treatment." In the sentence, treatment is singular, even though it discusses "animals in laboratories." Thus, the singular verb form "has become" is the correct answer.

The verb "hold" is a plural verb, but the subject of the sentence is the singular "The oldest." The verb needs to be changed to a singular form to be in agreement with the subject. The only answer choice that uses the correct verb is "the veterans holds a special place."

The underlined section of the sentence has a problem with the verb "have." While the verb is situated next to the plural noun "teenagers," the subject of the sentence is the word "each," which is singular. Therefore, the verb needs to be a singular form, and "Each of the teenagers has" is the correct answer choice.

The issue in the underlined portion of the sentence is that the sentence and verb are not in agreement. While the sentence references "classmates," that is in an interrupting phrase set off by commas, and the subject is the singular "teenager." "The teenager, along with her classmates, objects" is the correct answer choice.

The use of "are" is incorrect in the sentence, as it is a plural form and the subject of the sentence, "thing," is in the singular. The verb tense for "are" needs to be adjusted to the singular form; therefore, the correct answer is "is to listen."

The subject of this sentence, "A combination," is singular, so the predicate should be singular, too. The original text "delightfully entertaining plot twists characterize the novels of Jane Austen" and the answer choice "delightfully entertaining plot twists have characterized the novels of Jane Austen" contain plural predicates and therefore lead to subject-verb agreement errors. 

The answer choice "the fact that she twists the plot in delightfully entertaining ways characterizes the novels of Jane Austen" leads to faulty parallelism and the use of an ambiguous pronoun, and the answer choice "the fact that she twists the plot in delightfully entertaining ways characterize the novels of Jane Austen" leads to errors in both parallelism and subject-verb agreement.

Only answer choice "delightfully entertaining plot twists characterizes the novels of Jane Austen" correctly preserves the parallel structure and avoids any subject-verb agreement errors.