By conducting a national study of opioid abuse on college campuses, re

KAPLAN OFFICIAL EXPLANATION

(A)

Step 1: Read the Original Sentence Carefully, Looking for Errors

Because this sentence has a list in the underlined portion, determine whether that list has a parallel structure. The list is “where students purchase . . . how frequently students . . . and which college stressors . . . ” As written, the list has parallel structure, with each item beginning with a word—“where,” “how,” and “which”—that could begin a question (an interrogative adverb, if you’re curious) followed by a noun—“students,” “students,” and “college stressors,” respectively. Other elements worth checking are the modifying words “most commonly” before the verb “contribute” and the idiomatic usage of “contribute to.” All are correct.

Step 2: Scan and Group the Answer Choices

(A) and (B) begin with “which,” which is parallel to “where” and “how.” The remaining choices begin with elements that break the parallel structure.

Step 3: Eliminate Choices Until Only One Remains

(C), (D), and (E) are incorrect because they begin with a word that breaks the parallel structure of the list. (B) is wrong because it is unnecessarily wordy. The sentence here is correct as written, so (A) is the answer.