How will the right answer fit in terms of support and conclusion?

Only the right answer will add support for disagreeing with the conclusion.

Highlight the main conclusion in the passage, if there is one:

vitamin C has no real benefit in reducing the severity of acne.

[BACKGROUND]. [SUPPORT]. [SUPPORT]. [SUPPORT]. Therefore, we can tentatively conclude that [CONCLUSION].

There’s a lot going on here, so it’s a good thing you recognized that the conclusion is about cause-and-effect. In this case, the author says there isn’t a cause-and-effect relationship between vitamin C and acne. The right answer will support that there is.

Map the wording of the answers to the wording of the passage:

(A) …had a history of suffering from more severe acne…

Then they should still have “more severe acne” according to the author. But if “no difference” was found between the groups who didn’t mess everything up by knowing “which kind of pill they were given”, then you’d totally disagree that there’s no cause-and-effect happening.

(B) …took additional doses of vitamin C…

The author is claiming there’s “no real benefit” at all, so how big a dose someone took doesn’t really affect their conclusion.

(C) …lower than the national average.

Cool story, but the conclusion is only based on comparing the vitamin C takers to the placebo group. The “national average” is totally irrelevant.

(D) …that are naturally rich in vitamin C.

This is where recognizing the comparison really helps. Maybe you thought this “made sense”, but it only does if the subjects in the other group weren’t also consuming these foods. Valid comparisons have to give equal info about both sides, or it’s bunk. Like this answer choice.

(E) …did not actually take the pills…

Again, this adds info that’s only about one group. To make the comparison we need to know if subjects in the other group all took their pills or not. This answer leaves us to make our own assumption. Right answers never do that.

(A) is the correct answer.

Common pattern/s in this question: This is one really hard for sure, but no doubt that recognizing the comparison helps you avoid mistakes that are all too easy to make.