设备选型应遵循“先进、适用、经济”的原则。
参考答案：对
–Why do you look so happy?
--I got good grade in English exam. My teacher said .
A. I was hard-working B. I am a good students C. I have worked hard
电刷不得有损角或裂纹，电刷接触面不小于（）。
A、60—65%
B、70—75%
C、75—80%
D、100%
