Hi @OQ, thanks for your post. (A) is wrong because it does not accurately describe the stimulus author's reason for being skeptical of the researchers' claims.
Let's take a step back and assess for a moment. The stimulus presents an argument. The conclusion is "there is reason for skepticism," i.e., that we should be skeptical of the researchers' conclusion that "on average, 50-year-olds are more altruistic than 20-year-olds." What is the support given for the researchers' claim? They asked one hundred 50-year-olds about giving blood, and one hundred 20-year-olds the same question. Based on their answers, the researchers concluded that the 50-year-olds were "more altruistic" than the 20-year-olds. Why, according to the author of the stimulus, should we be skeptical of the researchers' conclusion? Because "many people hesitate to admit that their behavior does not conform to societal expectations."
This is "offering an alternative explanation of some of the data" - answer choice (B). The researchers explain the difference in answers between 50-year-olds and 20-year-olds by concluding that 50-year-olds are more altruistic. The author of the stimulus, however, points out that perhaps members of each group is trying to give the answer that "conforms to societal expectations."
The author of the stimulus does *not* argue that the researchers screwed up methodologically by deriving their data from a sample of subjects that is somehow unrepresentative. This is why (A) is incorrect.
Hope this helps! Please let us know if you have any additional questions.
