问题
单项选择题
直流电机的检查试验项目有：绕组对( )及绕组相互间绝缘电阻的测定，绕组在实际的冷态下直流电阻的测定，空载特性的测定和额定负载试验等。
A．导线
B．绝缘
C．气隙
D．机壳
答案
参考答案：D
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直流电机的检查试验项目有：绕组对( )及绕组相互间绝缘电阻的测定，绕组在实际的冷态下直流电阻的测定，空载特性的测定和额定负载试验等。
A．导线
B．绝缘
C．气隙
D．机壳
参考答案：D
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| Scientists think that there has been life on Earth for millions of years. However, we haven't found life __1 _ other planets yet. Scientists have discovered many other galaxies in the universe. They are a long way away and their _2_ has travelled for many years to reach us. Scientists have sent _3 of spacecraft to look at other planets in our solar system, and some spacecraft _4_ beyond the solar system. However, no one _5 discovered any life in space yet.
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