For logical reasoning style reading comprehension questions, first identify the question task, which in this case is to weaken the evidence.

Then, identify the conclusion of the argument to be weakened, in this case that colds are at least sometimes caused by becoming chilled.

Next, work through the choices looking for reasons to eliminate while considering the impact of the new information on the conclusion.

(A) If being chilled lowers the immune defenses, then it seems more likely that colds are caused by becoming chilled. This strengthens the argument, so eliminate Choice A as a reversal.
(B) If the first symptom of the cold is a feeling of chilliness, then the causation may be reversed in that the cold causes chilliness rather than the cold being caused by becoming chilled. This could weaken the argument, so keep Choice B.
(C) The variable of being tired is not discussed in the prompt, so eliminate Choice C for requiring additional information.
(D) Some people is a poorly defined variable that can be interpreted in numerous ways, so eliminate Choice D for having a vague impact.
(E) That a person could become chilled without catching a cold is an unclear hypothetical situation, so eliminate Choice E for also being vague.

Select Choice B for properly weakening the evidence for the conclusion that colds are at least sometimes caused by becoming chilled.