Which one of the following, if true, would most seriously weaken the argument in Homework #18?
A. Overripe vegetables are more nutritious than underripe ones.
(A) is incorrect. Recall that the argument in Homework #18 is that frozen vegetables are more nutritious than fresh ones, because they lose less of their nutritional value between the time they are picked and the time they are eaten. The stimulus there did express some concern that fresh vegetables picked ripe would be overripe by the time they reached the consumer, but the difference between overripe and underripe vegetables is not relevant to the argument. Even if this is true, it does not undermine the author's claim.
B. Vegetables destined for freezing and those destined for the grocery store are picked at the same time.
(B) is correct. The argument hinges on a distinction between what happens to vegetables between the time they are picked and the time they are eaten. Frozen vegetables, picked ripe, lose some nutrients in the freezing process, whereas fresh vegetables, picked early, lose even more by ripening off the vine. Therefore the point at which the vegetables are picked is important; how much nutritional value they lose depends in part on when they are picked. If both categories of vegetables are picked at the same time, then it is harder to argue that frozen vegetables are "better" than fresh ones.
C. Fresh vegetables are refrigerated during transport to prevent them from spoiling.
(C) is incorrect because it does not weaken the argument. The argument is not concerned with spoilage, but with loss of nutritional value caused by either freezing or ripening off the vine. This statement does not undermine the claim that ripe vegetables lose less nutrition when frozen than unripe ones do in transit from farm to store.
D. Many people who live near farms can purchase vegetables directly from the farmers.
(D) is incorrect because where people buy vegetables is irrelevant to the author's claims about the loss of nutritional value caused by freezing versus off-the-vine ripening. This statement does not make the author's conclusion, that one method causes less nutritional loss than the other, any less likely to be correct.
E. Tests have shown that fresh vegetables taste a lot better than frozen vegetables.
(E) is incorrect because it is also irrelevant. How the vegetables taste is not the issue; the issue is how nutritious they are when they are purchased and eaten.