听力题 Many people think that nothing happens when they sleep. Doctors have studied sleep for many years. They think that a lot happens when people sleep. Doctors say that people have five kinds, or stages, of sleep. People may go through each stage about every 10 minutes. During the first two stages, you sleep lightly. That is, if someone calls you or puts his hand on you, you wake up quickly. Your body rests quietly, you breathe more slowly than when you are awake. Your heart beats slowly. During stages three and four, you sleep deeply. That is, if someone puts his hand on you, you don’t wake up. Your heart beats more slowly than that in stages one and two. You don’t hear sounds. Lights don’t wake you up. The last stage of sleep is called REM (Rapid Eye Movement). During REM sleep you breathe faster, and your heart beats faster than that in stages one through four. Your eyes move under your eyelids. All of this happens because you are dreaming. Doctors say that everyone dreams. Some dreams are short; some dreams are long. Some people are good at remembering their dreams; others forget theirs.