路由器具有数据通道功能和()通道功能。
A.管理
B.检测
C.控制
D.维护
参考答案:C
—English is______ too difficult for me. I can't learn it well.
—Don't give up. Nothing is difficult if you work hard. [ ]
A. seldom
B. usually
C. never
D. always
三相异步电动机的工作原理是什么?