(A) Given that the argument is based on the idea that social interaction is itself exercise, this statement is line with the conclusion of the argument.

(B) The conclusion of the argument is based on the idea that there is a cause and effect relationship between social interaction and mental and perceptual skills. This answer choice weakens the argument by indicating that the relationship may not be causal one but rather merely a correlation. Social interaction and mental alertness are both effects of better health.

(C) This answer choice does not really have much relevance to the argument, but if a person were looking for an answer that sounds right and not really considering logic, the person might choose this choice.

(D) This does not make much difference. The study used data. That the data came from other studies does not weaken conclusions based on that data. This is another choice that might be tempting to someone who is not really paying attention to what is being said.

(E) What a great trap answer. The point of the argument is that social interactions increase mental sharpness, and the mental sharpness mentioned in the argument is not somehow restricted to skills used in social interactions.

The correct answer is B.