This question is a strengthen with a necessary premise question, so if the negation of an answer choice wrecks the argument, then we know that it's the correct answer choice.
(B) says, "anyone who does not serve on a medical review panel does not have the necessary knowledge and expertise to evaluate medical research findings"
(B)'s negation is, "Anyone who does not serve on a medical review panel still might have the necessary knowledge and expertise to evaluate medical research findings."
(B)'s negation does not wreck the argument. The premises of the argument already inform us that a peer review panel is necessary in order to evaluate the findings. However, why it's needed (whether it's expertise, knowledge, or some other reason) is something that doesn't matter for us. Thus, (B) is out.
(A) says, "unless medical research findings are brought to peer review by a medical journal, peer review will not occur"
(A)'s negation is, "Peer review of medical research findings does not require publication in a medical journal."
(A) does a great job in capturing the necessary assumption that the conclusion is jumping toward (peer review needs a medical journal). However, if peer-reviewed findings could be published in other places (which is what the negation says), then the argument falls apart, which tells us that (A) is the correct answer choice.
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