单选题
On the part of an average sleeper, there ______ of sleep in cycles.
A、
is one stage
B、
are two stages
C、
are six stages
D、
are four stages
【正确答案】
D
【答案解析】
[分析] 细节题型。 答案出自第一段第二到第六句Your brain waves slow down...for the first few minutes．This is the first stage of sleep. ...you will reach the last stage．
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