The error in the underlined portion of the sentence is its use of the singular form "part" after the adjectives "many different." As both adjectives indicate the plurality of the noun they describe, the singular noun "part" needs to be a plural noun to correct the error. "Many different parts of the world" is the correct answer choice because it is the only one in which this error is corrected.

The key issue with the underlined phrase is the simultaneous use of "an" and the plural form "studies." Either the singular "an" or the plural "studies" needs to be changed to make the forms match. "An objective study" is the correct answer choice.

Since we are talking about "dogs" (plural), they must have "mates" (plural). Also, “their” is the possessive form of “they.” “There” denotes a place, and “they’re” is the contraction of “they are.”

Because the pronoun in the next sentence is describing the "shoes," plural, the pronoun must be the plural "they." The verbs must also then follow the plural form "squeak and squish," making the correct answer "they squeak and squish when I walk." Note that a semicolon is correctly used to separate the two independent clauses making up this sentence, and also note that since the two clauses are combined into one sentence, the pronouns must remain consistent within that sentence, even though each clause is independent.

The plural "classmates" were suggesting, so he had to receive plural "suggestions." Also, since he "moved" (past tense) we have to say that the classmates "gave" (past tense) the suggestions. This means the correct answer is "gave me suggestions for how to make friends."

"To Timmy, the best part of science fiction movies is the special effects."

This is the only correct answer because the subject ("part") agrees in number with the verb ("is"). Do not be misled by the plural "movies"; it is not the subject.

This is a case in which we need to decide whether to use the word "which" or "that" to introduce the clause set apart from the rest of the sentence by commas. "That" is used to introduce information absolutely necessary to the sentence's meaning, whereas "which" is used to introduce information that would not change the sentence's meaning if it were removed from the sentence. Information that is not crucial to the sentence's meaning is usually set apart by commas.

In this case, the sentence "The last time it snowed, my dad lost control of his car and hit a tree" still makes sense, so we know that the information included between the commas isn't absolutely necessary to the sentence's meaning. Plus, the information in question is being set apart from the rest of the sentence by commas. So, we should use "which," and not "that."

Because the second independent clause contradicts the first in this compound sentence it is more correct to separate the two with the conjunction "but," not "and."

Only answer choice "the heroine, Catherine, must choose between true love and social preeminence" correctly uses "and" with the preposition "between."

The other answer choices, including the original text "the heroine, Catherine, must choose between true love or social preeminence," contain an incorrect idiomatic expression. When we have "between," we typically need the word "and"—rather than "or"—to separate the entities that follow.

In standard English, when you use the phrase "not only" in a sentence, it should be followed by the phrase "but also." So, the correct answer is "When she went to the zoo, Lyndsey got to see not only tigers, but also polar bears, iguanas, and toucans."