Choice B is the best answer because it most logically completes the text’s discussion of behavioral psychology studies. In this context, “ameliorate” means to help remedy or improve. The text states that many behavioral psychology studies are flawed because the subjects used are “highly unrepresentative.” It is then suggested that researchers should recruit subjects from “diverse backgrounds and locations” in order to help address the issue of unrepresentative subject pools. Thus, this context conveys that recruitment efforts focused on diversity would help ameliorate the problems outlined in the text.
Choice A is incorrect. In this context, “sanction” could have two meanings: to give official approval for something or to enact a penalty, neither of which makes sense in this context. The text describes a situation known to be problematic in behavioral psychology studies and then presents a potential remedy to that situation; the text does not suggest that the situation is officially approved or results in any type of penalty. Choice C is incorrect because rather than “rationalize,” or explain or justify, a situation, the text presents a situation and its potential remedy. Choice D is incorrect because the text is not attempting to “postulate,” or suggest a claim or theory, related to the situation described in the text but is rather presenting a potential remedy for the situation.