单选题 Researchers have found that REM (rapid eye movement) sleep is important to human beings. This type of sleep generally occurs four or five times during one night of sleep lasting five minutes to forty minutes for each occurrence. The deeper a person's sleep becomes, the longer the periods of rapid eye movement.
There are physical charges in the body to show that a person has changed from NREM (non-rapid eye movement) to REM sleep. Breathing becomes faster, the heart rate increases, and, as the name implies, the eyes begin to move quickly.
Accompanying these physical changes in the body is a very important characteristic of REM sleep. It is during REM sleep that a person dreams.

单选题 According to the passage, how often does REM sleep occur in one night?

A. Once
B. Twice
C. Four or five times
D. Forty times

【正确答案】 C

【答案解析】[解析] 参见文章第二句。

单选题 The word "deeper" in Paragraph 1 is closest in meaning to which of the following?

A. heavier.
B. louder.
C. stronger.
D. happier.

【正确答案】 A

【答案解析】[解析] heavy和deep一样可用于修饰人的睡眠，且意思相近。

单选题 Which of the following shows that a person is NOT dreaming in his sleep?

A. His eyes begin to move.
B. His breathing becomes faster.
C. His heart rate increases.
D. His eyes stop moving.

【正确答案】 D

【答案解析】[解析] 参考文章第二段和第三段，人在睡眠的REM阶段会做梦，而呼吸加快、心率升高和眼球运动是人从NREM阶段转入REM阶段的标志。

单选题 The subject of this passage is ______.

A. why people sleep
B. the human need for REM sleep
C. the characteristic of REM sleep
D. physical changes in the human body

【正确答案】 C

【答案解析】[解析] 文章主要介绍的就是人在REM阶段的各种表现。