Mismatched premises. (A) doesn’t involve pointing out that most instances might not support a conclusion. Rather, (A) points out that we need to wait for more information before drawing a conclusion.

(B)’s conclusion asserts that it’s unreasonable to think something is effective. But the conclusion in the stimulus asserts only that it’s unreasonable to hold a certain belief based on a particular premise; it doesn’t assert that the belief itself is unreasonable without regard to why someone holds that belief. (There’s a difference between saying “X is unreasonable” and “X is unreasonable to believe based on Y.”)

(C)’s conclusion asserts that it’s unreasonable to think that something causes cancer remission. But the conclusion in the stimulus asserts only that it’s unreasonable to hold a certain belief based on a particular premise; it doesn’t assert that the belief itself is unreasonable without regard to why someone holds that belief. (There’s a difference between saying “X is unreasonable” and “X is unreasonable to believe based on Y.”)

This involves a conclusion that it’s unreasonable draw a certain conclusion (that aspirin is dangerous) based on the fact there are some instances that support that view (a number of people who die prematurely take aspirin). Why? Because most instances do not support that view (most people who take aspirin do not die prematurely).

(E) involves a conclusion that there is a causal connection based on some instances that provide evidence of it. But the argument in the stimulus was cautioning against drawing a causal connection.