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How Much Sleep Do We Need?何曼婷个人资料
  Sleep, as we know, is important to us because it helps 光头佬麦嘉>精忠报国 伴奏restore（恢复）tired organs（器官）and tissues（组织）in our body. But how much sleep do we actually need?
印子月    For most of us, eight hours seems to be about the right amount. Yet we know that there are a great many people who get along perfectly with less sleep and some who may even need more. A great deal depends on the way we live. But a good general rule to follow is to sleep as long as we have to in order to feel happy and be able to work at our best when we awaken.
    There are actually different levels of sleep. There is a deep sleep and a shallow sleep. In a shallow sleep, our body does not get the same kind of rest it gets in deep sleep, so that after eight hours of a shallow sleep we may still feel tired. But a short, deep sleep can be very restful（宁静的）.
    Alexander the Great was able to get a deep sleep whenever he needed it. Once, during the night before an important battle, he remained awake longer than anyone else. Then he wrapped himself in a skeeter daviscloak（宽大外衣）and lay down on the earth. He slept so deeply that his generals had to wake him three times to give the command to attack!
Normally when we go to sleep, our “sleep centre” blocks off（阻挡，隔开）nerves so that both our brain and our body go to sleep. One prevents us from wanting to do anything, and the other makes our internal organs and limbs（四肢）go to sleep. But sometimes only one goes to sleep and the other does not. A very tired soldier can sometimes fall asleep (brain sleep) and keep on marching, because his body is not asleep!
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