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问题 多项选择题

绕线式三相异步电动机可以采用( )进行调速。

A．改变电源频率f

B．改变额定电压UN

C．改变额定电流IN

D．改变转子磁极对数P

E．改变转差率S

答案

参考答案：A,D,E

填空题
根据句意从方框中选用合适的词组，并用其适当形式填空。
in general; to go somewhere; take it easy; some day;
as soon as possible
1. I'd like _____ to have a rest.
2. I hope to visit the Great Wall _____. 
3. Why do some students want to start work _____? 
4. I like games _____, and especially football.
5. _____,  you had better do it one by one.
21. to go somewhere  22. some day 23. as soon as possible  24. in general 25. Take it easy
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问答题

如图所示是研究“决定压力作用效果的因素”的实验装置图．通过观察分析甲、乙两次实验，可以得出结论：______．
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