Explanation
Creating a filter: We read the sentence and, drifting to
the answer choices, see a 3 versus 2 standoff of "whether" against "if." This
is a yes-or-no question, not a condition, so "whether" is correct and "if" is
incorrect. We'll filter for choices that use "whether."
Applying the filter: our filter leaves us with (A) through
(C).
Finding objective defects: choice (B) introduces an
ambiguous pronoun "they," which seems to indicate that veterans are
administering the drug, contrary to intended meaning. Choices (A) and (C) are
similar. Which conveys the intended meaning? We can see that (A) is
imprecise and (C) is precise. Contrary to the intended meaning, (A) makes it
sound as if we might be wondering whether the new drug will have an effect before
it's administered, or during its administration. The administration is
meant to be the precondition for the intended effect. The word "once" and the
verb tense "has been" both do that accurately. Here the present perfect verb
"has been administered" is fitting, because we want to convey that the
administration occurs right before the effect will or will not be seen. The
correct answer is (C).
If you believe you have found an error in this question or explanation, please contact us and include the question title or URL in your message.