阅读理解
After a day of work and play, the body needs to rest. Enough sleep is necessary for good health. During this time, the body recovers from the activities of the previous day. The rest that you get while sleeping enables your body to prepare itself for the next day. There are four levels of sleep, each being a little deeper than the one before. As you sleep, your muscles relax little by little. Your heart beats more slowly, and your brain slows down. After you reach the fourth level, your body shifts back and forth from one level of sleep to another. Although your mind slows down, from time to time you will dream. Scientists who study sleep state that when dreaming occurs, your eyeballs begin to move more quickly (Although your eyelids are closed). This stage of sleep is called REM, which stands for rapid eye movement. If you have trouble falling asleep, some people recommend that you breathe very deeply. Other people believe that drinking warm milk will help make you drowsy. There is also an old suggestion that counting sheep will help you fall asleep!
单选题
The word drowsy in the last paragraph means______.
【正确答案】
D
【答案解析】最后一段讲述有助于睡眠的方法。根据最后一段最后一句“…will help you fall asleep!”可推知，drowsy是fall asleep的近义词。sick：生病的，病态的；awake：醒着的；asleep：睡着的，长眠的；sleepy：困乏的，欲睡的。根据句意“其他人认为喝杯热牛奶将有助于让你有困意”可知，选D。
单选题
This passage suggests that not getting enough sleep might cause you to______.
【正确答案】
B
【答案解析】根据第一段第二句“Enough sleep is necessary for good health．”可知，充足的睡眠对健康很有必要。由此可推知，不充足的睡眠可能会导致健康情况很糟糕。故选B。A、C两项内容文章并未提及，D项是有助于睡眠的方法。
单选题
According to the passage, during REM,______.
【正确答案】
D
【答案解析】根据第三段第二句“…when dreaming occurs，your eyeballs begin to move more quickly…”可知，当人们做梦时，眼球开始快速转动，这个过程叫作REM。因此选项A、B都正确。故选D。
单选题
The average number of hours of sleep that an adult needs is______ .