问题
单项选择题
三相异步电动机接通电源后启动不起来，转子左右摆动，有强烈的“嗡嗡”声是由于（）。
A、电源一相断开
B、电源电压过低
C、定子绕组有短路
D、原因不定
答案
参考答案：A
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三相异步电动机接通电源后启动不起来，转子左右摆动，有强烈的“嗡嗡”声是由于（）。
A、电源一相断开
B、电源电压过低
C、定子绕组有短路
D、原因不定
参考答案：A
根据短文内容，用方框里所给词的适当形式填空，每词限用一次
A washing machine helps us to wash clothes. A printing machine helps us to__4__ a lot of books, news papers, magazines and many __5__ things quickly. Bicycles, cars, trains and planes are all __6__ , too. They help us to travel faster than on foot. The computer is a wonderful machine. It was __7__ not long ago. It not only stores information but also numbers millions of times as __8__ as a scientist does. Let's study hard and try to use all __9__ of machines. I think we can build China into a __10__ country in the future. |