单项选择题

Stage 4 sleep lasts______.

A．about 80 minutes
B．about 40-60 minutes
C．about 30 minutes
D．about 20-40 minutes
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单项选择题
One of the features of REM sleep is that______.
A．there are large slow waves, though rapid for the first few minutes
B．you have the deepest sleep
C．there are no brain waves
D．the brain waves are a little fast and the brain becomes a little active
单项选择题
If you followed the advice of the writer, you would______.
A．weigh carefully what people say to determine their real meaning
B．get along well with people
C．trust what other people say
D．have no doubts about our friends
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