我们的身体夜晚需要休息，白天需要清醒。大多数人每晚需要8到8.5个小时的睡眠才能正常运转。找到更多的时间、更好的睡眠方法可能是个挑战。科学家已经确认了80多种不同的睡眠紊乱症(sleep disorders)。有些睡眠紊乱症是遗传的。但是，许多睡眠紊乱症是由于熬夜，经常跨时区旅行以及上夜班而引起的。

参考译文： 英语四级词汇表下载

Sleep Disorders

Our bodies want to sleep at night and be awake during the day. Most women and men need between eight and eight and a half hours of sleep a night to function properly throughout their lives.Finding ways to get more and better sleep can be a challenge. Scientists have identified more than 80 different sleep disorders. Some sleeping disorders are genetic. But many problems are caused by staying up late and by traveling frequently between time zone or by working nights.