问题
单项选择题
直流电动机主磁极的作用是（）。
A、产生主磁场
B、产生电枢电流
C、改善换向性能
D、产生换向磁场
答案
参考答案：A
搜题请搜索小程序“爱下问搜题”
直流电动机主磁极的作用是（）。
A、产生主磁场
B、产生电枢电流
C、改善换向性能
D、产生换向磁场
参考答案：A
| 根据句意，从方框内选择合适的单词或短语，并用其适当形式完成句子。 | |
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| 1. Why didn't you ___________ until 7 pm yesterday? 2. When we __________ out, the thief had already run off. 3. Have you ever __________ your keys in your room? 4. I am sorry that all the tickets for the day have been __________. 5. Lily 's race-car __________ halfway. She had to give up the race. |