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问题 单项选择题

如果飞机上使用了晶体管调压器，当发电机端电压发生变化时：（）.

A.改变晶体管功率导通比以调节励磁电流

B.调节发电机的转速

C.在励磁电路中串联一电阻，调节励磁电流

D.晶体管必须工作在放大区

答案

参考答案：A

填空题

单词拼写。

1. They do not d_____ the mail that their customer specifically requests to receive.

2. She wanted to i_____ her students by having them listen to this instructive speech.

3. You didn't tell me you could sing so well-you're very m_____.

4. C_____ is difficult when two people don't speak the same language.

5. She d_____ her life to helping the poor.

6. The teacher was pleased with the children's good _____ (举止).

7. The car was cheap and in good _____ (状况), so I bought it.

8. She has a big family to _____ (赡养).

9. He worked hard and _____ (实现) his aim of becoming a doctor.

10. Please be more _____ (考虑周到的) and don't play loud music late at night.

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选择题

同步卫星是指相对于地面不动的人造地球卫星（　　）

A．它可以在地面上任一点的正上方，且离地心的距离可按需要选择不同值

B．它可以在地面上任一点的正上方，但离地心的距离是一定的

C．它只能在赤道的正上方，但离地心的距离可按需要选择不同值

D．它只能在赤道的正上方，且离地心的距离是一定的
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