短文填空  先通读下面的短文，然后根据短文内容和所给首字母，在空格内填入一个适当的词，使短文意思完整，所填单词必须在答卷标有题号的横线上完整写出。（本大题共5分，每格0.5分）
Are you sometimes a little tired and sleepy in the early afternoon? Many people feel this way after lunch. They may think that eating lunch is the c of the sleepiness. Or, in summer, they may think it is the heat. However, the real reason lies inside their b  . At that time — about eight hours after you wake up — your body t   goes down. This is what makes you slow down and feel sleepy. S   have tested sleep habits in experiments where there was no night or day. The people in these experiments also always f   a similar sleeping pattern. They slept for one long period(期间) and then for one short period about eight hours later. In many parts of the world, people take naps(小睡) in the middle of the day. This is e    true in warmer climates, where the heat makes work d  in the early afternoon. Researchers are now saying that naps are g   for everyone in any climate. A daily nap gives one a more rested body and mind and therefore is good for health in general. In countries where naps are t     , people often suffer less from problems such as heart disease. Remember that the best time to take a nap is about eight hours after you get up. A short sleep too late in the day may only make you feel more tired and sleepy afterward. This can also h   if you sleep for too long. If you do not have enough time, try a short nap,even ten minutes of sleep can be helpful.