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问题 选择题

已知cosα＜0.5，那么锐角α的取值范围是（　　）

A．60°＜α＜90°

B．0°＜α＜60°

C．30°＜α＜90°

D．0°＜α＜30°

答案

∵cos90°=0，cos60°=0.5，

又∵0＜cosα＜0.5，

∴60°＜α＜90°．

故选A．

填空题

根据首字母提示完成短文。

     Sanya, Harbin and Beijing are three c      in China, and they are in different

places. They are quite f        from each other. Sanya is in Hainan Province and

it's in the w       place of China. Even in winter, it's about 15℃ in the  daytime.

Harbin is in the n             of China. It's cold in w        . sometimes －30℃.

There is an Ice and Snow Festival that lasts six w           . Beijing is not very

cold in winter. It's about -5℃. It doesn't o       ram or snow. The p       of hotel

rooms are quite different, too. In Beijing hotels usually cut t       prices in

winter. About 200 yuan a night is e           .

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单项选择题

直流励磁机励磁系统的优点是（）。

A、控制方便

B、是静止的

C、无接触磨损

D、电压响应速度快
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