题目内容：
根据下面内容，回答题：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 toforty minutes for each occurrence. The deeper a person's sleep becomes, the longer the periods ofrapid 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 thename 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.
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