Going to sleep may seem quite boring compared with all the fun things you do while you are awake, but there's a lot going on in your mind and body while you are sleeping.

Sleep, in fact, is as important to your survival（生存） as eating and drinking. Sleep improves your mood, makes you a better athlete and helps you remember and understand what you learned during the day. While you sleep, your body temperature drops. Your heart beats more slowly, A chemical that controls growth, which is called a hormone(荷尔蒙),moves into your bloodstream. Scientists think that sleep brings back energy and improves your immune (免疫)system.

Sleep is like a school day: it's divided into different stages. When you are awake, your brain waves move quickly. As you begin to relax and fall into the first stage of sleep, your brain produces slower-moving waves and you lose awareness (意识) of your surroundings（环境）．As you fall into deeper sleep, your body repairs itself from the normal wear and tear of daily life. Then, as you begin to drift back into a lighter sleep, your mind becomes more alert(警觉的), and your dreams begin. You are in REM sleep.

REM is the name for the rapid eye movement that happens while you are dreaming. During REM sleep, your eyes move back and forth behind, as though you were watching a movie.

During other stages of sleep, you might move in bed, but during REM sleep you're not making any movement, That's probably because if you could move, your body would act out your dreams. As you get closer to waking up in the morning, you spend more time in REM sleep than in deep sleep, so you dream more. Researchers know that during REM sleep the part of the brain that deals with learning and thinking is very active.

Getting too little sleep can affect your personality. Experts recommend that children get at least nine hours of sleep a night.

50. Which is the right order during your sleep?

　 ① your body repairs itself from the normal wear and tear of daily life

　 ② your brain produces slower-moving waves

　 ③ your dreams begin

　 ④ you lose awareness of your surroundings

　 A.①③②④　　　　 B.②④①③　　　 C.④①③②　　　　 D.②④③①

51. In which of the stage/stages of sleep do you have the most dreams?

　　 A. Light sleep. B. Deep sleep.

C. REM sleep.　 　　　　　　　　　　　　 D. The first two stages of sleep.

52. Which of the following is NOT true?

　　 A. You don't move while you are dreaming in REM sleep.

　　 B. During REM sleep, the whole brain is active.

　　 C. The closer to waking in the morning, the more dreams you have.

　　 D. Hormones have something to do with your growth.

53. According to the scientists and experts, _______.

A. adults get at least nine hours of sleep a night

　　 B. there's nothing going on in your mind while you're sleeping

　　 C. sleep have little impact(影响) on our personality

　　 D. sleep can make us energetic and healthy