单选题
Which of the following does the passage mainly discuss?
A、
Scientific methods of studying sleep.
B、
Why humans require sleep.
C、
The phases of sleep.
D、
Why dreams occur during REM sleep.
【正确答案】
C
【答案解析】
[解析] 这段阅读主要讲的是睡眠的各个阶段。文中讲睡眠有四个阶段，各阶段有其各自的特点。
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