Explanation

Reading the question: we read the prompt and find a somewhat hasty argument. The first two statements are facts, while the last one is an opinion and is the conclusion. One weakness here is that the author has allowed for only two possibilities. There might be another possibility. And that makes us notice: we have a causal argument! So we will look for a different cause in the answer choices--for the increased percentage of adults who have seen a doctor for gluten allergies. Specifically, given the format of the answer choices, which one rules out a new cause for increased visits? That's our filter.

Applying the filter: (A), (B), and (E) all rule something out, but the things they rule out wouldn't cause more gluten visits. Choice (C) rules out something that would cause more gluten visits, so it looks correct.

Logical proof: Negating (C) proves it: if people with the allergy are more likely to go in, that could be a different reason than given in the conclusion and the argument would be weakened or broken. Meanwhile, choice (D) does not pass the negation test; it merely states a possibility. The correct answer is (C).