【正确答案】 D

【答案解析】[听力原文] Do you find yourself tired all the time although you get enough sleep? Then maybe this is for you. When you're feeling weak and tired, the worst thing to do is to take a nap. It won't restore your stamina. On the contrary, what happens then is your body loses even more energy than it had before, making you even more sleepy. You may also have these poor habits that worsen the problems. Do you stay in the same small area without getting up to move around? Does your job require that you sit down the whole day in front of a computer? Any of all of these reasons might be the cause of your energy loss, keeping your energy level low. What should you do, then, at those moments when you feel so tired even though you've gotten enough sleep? A cup of coffee won't help much either, as it is easy to get addicted to the caffeine. The best and most natural thing to do is to take a brisk walk. Doctors recommend the activity because it will increase the heart rate. This increased heart rate will lead to several hours of alertness. Moreover, a regular exercise routine can make your fatigue problems disappear forever. Until tomorrow, this has been another broadcast in our special program: 'A Healthy Body'. Tomorrow, our discussion will focus on sleeping problems. What is the main topic of the passage?