月经周期中雌、孕激素对丘脑下部及腺垂体的反馈作用表现为（）。

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问题多项选择题

A.雌激素有正反馈作用

B.孕激素有正反馈作用

C.雌激素既有正反馈又有负反馈作用

D.孕激素有负反馈作用

E.孕激素既有正反馈又有负反馈作用

答案

参考答案：A, C, D

单项选择题

Have you ever heard your own voice "Of course," you say.
Has anyone else ever heard your voice Again you say, "Of course. "
But that’ s not quite true. Nobody else has ever heard your voice—the way you hear it. When you talk, you set up sound waves. The air outside your head carries the sound waves to your outer ears. But, of course, the sound of your voice begins inside your head. The bones of your head pick up the sound waves, too. They carry the sound waves straight to your inner ears. You get the sound from the outside and the inside too. Other people get just the sound waves from the outside. That’s why they don’t hear your voice the way you do.

Sound travels in the form of ______.

A．bones

B．air

C．waves

D．voice

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单项选择题

西班牙内战演变为反法西斯的民族革命战争，主要是由于( )。

A．法西斯军官发动叛乱
B．国际纵队的直接参战
C．德、意公开武装干涉
D．英、法采取不干涉政策

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