[简答题]Rapid eye movement sleep is sometimes called paradoxical sleep because it has A B characteristics of either the waking and sleeping states. C D

[单项选择]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 changes 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 there is a very important characteristic of REM sleep. It is during REM sleep that a person dreams.
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

[填空题]Sleep is divided into periods of so-called REM sleep, characterized by rapid eye movements and dreaming, and longer periods of non-REM sleep.　________　kind of sleep is at all well-understood, but REM sleep is　________　to serve some restorative function of the brain. The purpose of non-REM sleep is even more　________　. The new experiments, such as those　________　for the first time at a recent meeting of the Society for Sleep Research in Minneapolis, suggest fascinating explanations________of non-REM sleep. 　　For example, it has long been known that total sleep________is 100 percent fatal to rats, yet, ________examination of the dead bodies, the animals look completely normal. A researcher has now　________　the mystery of why the animals die. The rats　________　bacterial infections of the blood,　________　their immune systems the self-protecting mechanism against diseases―had crashed.
A. A． paid attention to
B． caught sight of
C． laid emphasis on
D． cast light on