McKinley says a double-blind study is the "best" way to test new drugs, not the "only" effective way. More importantly for this question, nothing in Engle's statements indicates that he interprets McKinley's argument as assuming double-blind studies are the only effective way. He accuses McKinley of assuming the study's outcome in advance, and counters McKinley's conclusion that a double-blind study is impossible in this case, but never says anything about double-blind studies compared to other means of testing drugs.

Engle accuses McKinley of assuming he knows the outcome of the study. Though he doesn't specify what he thinks McKinley assumes the outcome will be, since Engle interprets McKinley's reference to certain "effects" of the drug as assuming "the outcome" of the study, it seems likely that, if anything, Engle thinks McKinley assumes the drug will visibly have its intended effect. Engle certainly doesn't claim anywhere that McKinley denies the effectiveness of the drug.

This is a very tricky answer choice, because it comes close to paraphrasing what is actually a necessary assumption in McKinley's argument. While McKinley doesn't necessarily assume the placebo will have "no effects whatever" on the patients' bodies, his argument certainly assumes that the placebo will not have the same effects on the patients' bodies as the drug does.

But, though this is a real gap in McKinley's argument, it's really important to see that Engle doesn't actually suggest this gap. Remember that Engle's premise is that McKinley assumes he knows the "outcome" of the study. From the stimulus, we know the study's "outcome" is supposed to show whether or not the drug is effective, so we know Engle thinks McKinley is saying that the "effects" that show up will indicate whether the drug is effective. But Engle's argument doesn't claim, or even imply, that McKinley believes the placebo will have no effects: Engle could certainly interpret McKinley as thinking the placebo will have some effects, just not effects that would be the same as the drug's effects.

To sum up, this answer choice says some of the right things — but even as a necessary assumption, it fails because it's too restrictive. More importantly for this question, even if this answer choice did accurately identify a flaw in McKinley's argument, the fact that Engle's argument is not about this flaw should disqualify this answer choice.

This is correct. All McKinley mentions are "various effects" the drug will have on patients' bodies. Engle interprets this to mean that McKinley assumes the "outcome" of the study will be clear from these effects. We know the outcome of a double-blind study is to show whether a drug is effective. So Engle clearly thinks the "effects" McKinley refers to aren't just "side effects," unrelated to the drug's therapeutic efficacy. Engle must think that the "effects" McKinley mentions are effects that reveal whether the drug is effective — i.e., therapeutic effects of the drug.

Engle doesn't accuse McKinley of being confused about when a drug is efficacious — whether that means not knowing when a drug's effects actually occur, or not knowing the criteria for when a drug can be considered "efficacious." Rather, Engle accuses McKinley of assuming he knows, ahead of time, that this drug is efficacious. But wrongly assuming you know ahead of time whether something is efficacious or not in a specific case doesn't imply confusion about what "efficacy" means, or when that label applies.