Answer: A

This is an evidence question. The argument is that there are societal benefits to the use of mind-enhancing drugs, such as giving poor students an advantage on university admissions exams. We're looking for a piece of evidence that, affirmed or denied, would strengthen or weaken the argument:

(A) This is correct. The argument admits that there are risks in using certain substances, but then focuses on the possible benefits. If the risks outweigh the benefits, the example seems much weaker, and there is a reason to "categorically avoid mind-enhancing drugs."
(B) The argument focuses on benefits accruing to poor students. If the same benefits can be had by richer students, that doesn't affect the fact that poor students using certain substances can study more effectively with them.
(C) This is irrelevant, as the benefit referred to in the argument is based on "the responsible use of these substances."
(D) This is outside of the scope, as it only touches a couple of areas, while it seems logical that most areas would benefit from being able to "concentrate longer and focus better."
(E) The argument focuses on performance on admissions exams; while it is natural to link those to actual admissions decisions, it is outside the scope of this argument.