单项选择题

The brain waves are the slowest during______.

A．stage 1
B．stage 2 and stage 3
C．stage 4
D．REM sleep
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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
单项选择题
When the writer recalls the things that happened between him and his friends, he ______.
A．feels happy, thinking of how nice his friends were to him
B．feels he may not have "read" his friends' true feelings correctly
C．thinks it was a mistake to view Jim as a friend
D．is sorry that his friends let him down
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