A Brain Exercise is where you answer a question about health. Option B
A brain exercise is completing a cognitive task, such responding to a health-related query. Cognitive fitness is enhanced by mental exercises that test one's ability to recall information, solve problems, and think critically.
While the brain may be stimulated differently by physical exercises like jumping jacks and sensory experiences like rubbing your head, answering a question is a unique example of a mental or brain exercise because it requires higher-order cognitive operations.