异步电动机按转子的结构不同分为笼型和()两类。
A.绕线转子型
B.单相
C.三相
D.以上都不是
参考答案:A
___ most of the earth’s surface is covered by water, fresh water is very rare and precious.
A.As
B.Once
C.If
D.Although
下列哪一组牙不是替换牙?()
A.切牙
B.尖牙
C.前磨牙
D磨牙