2009年6月英语六级阅读冲刺倒计时(倒数15天)英语六级考试
文章作者 100test 发表时间 2009:07:07 21:23:58
来源 100Test.Com百考试题网
We all know that the normal human daily cycle of activity is of some 7-8 hours’ sleep alternation with some 16-17 hours’ wakefulness and that, broadly speaking, the sleep normally coincides with the hours of darkness. Our present concern is with how easily and to what extent this cycle can be modified.