问题
单项选择题
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
答案
参考答案：D
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．