单选题

　　[阅读选择]Physiologically， we are rhythmical. We must eat， sleep， breathe， and play regularly to maintain good health. Emotionally we are rhythmical， too， for psychologists say that all of us feel alternate periods of relative depression and exhilaration. Intellectually we are also rhythmical， for we must have periods of relaxation following periods of concentration. It naturally follows then that rhythm， a fundamental aspect of our lives， must be a part of any good literary work——whether poetry or prose.

　　According to the passage， which of the following pairs of activities best illustrates intellectual rhythm？

　　A.Studying a science book and then studying a psychology book

　　B.Learning a poem and then taking a nap

　　C.Playing ball at the beach and then going swimming

　　D.Solving a math problem and then solving a chemistry problem