The physician says that a study should only be permitted if it is likely to reveal information about an important medical condition and it is known to pose only a minimal risk the subject. If either of these conditions is false, then the study should be prohibited.
reveal information AND minimal risk = allow not reveal information OR not minimal risk = prohibit
(A) is incorrect because it fails to address either of these conditions, rather it talks about resources being better used elsewhere - that is not one of the arguments that the physician makes. (E) on the other hand points out that the long term effects have never been tested, hence "it is known to pose only a minimal risk to the subject" condition is false, allowing the physician's conclusion that the study should be prohibited to follow logically.