标签：话题作文 话题 高中英语作文
字数：2000字
提要： there is some evidence that the two types of sleep, dreaming and dreamless, depend on the life-style of the animal, and that predators are statistically much more likely to dream than prey, which are in turn much more likely to experience dreamless sleep. in dream sleep, the animal is powerfully immobilized and remarkably unresponsive to external stimuli. dreamless sleep is much shallower, ..