1995年全国硕士研究生入学统一考试英语试题Section Use of EnglishSleep is divided into periods of so-called REM sleep, characterized by rapid eye movements and dreaming, and longer periods of non-REM sleep. 1 kind of sleep is at all well-understood, but REM sleep is 2 to serve some restorative function of the brain. The purpose of non-REM sleep is even more 3 . The new experiments, such as these 4 for the first time at a recent meeting of the Society for Sleep Research in Minneapolis, suggest
