[originaltext] (19)Do you have a tough math test coming up? Then listen to s

(19)Do you have a tough math test coming up? Then listen to some classical piano music just before the test. You might end up with a higher score. Researchers at a university in California conducted an experiment. They asked a group of college students to listen to some piano music by a famous 18th century composer before taking a math test. They were surprised to find that the students’ scores jumped 8 to 9 points. (20)The music seems to excite nerve activities in the brain similar to the activity that occurs when a person is figuring out a math problem. However, the scientists warn that before you get too excited about applying this method to your math test, (21)you should remember that brain-exciting effects last only 10 to 15 minutes. Would rock music work as well as the piano music did? No, the scientists say. In fact, the less complex music might even interfere with the brain’s reasoning ability.
19. What is this passage mainly about?
20. Why can classical music play a positive role in problem solving?
21. What is one of the findings of the research?