编制有序用电方案的原则是()。
A.先避峰,后错峰,再限电,最后拉闸
B.限电不拉闸
C.先错峰,后避峰,再限电,最后拉闸
D.先错峰,后避峰,再限电,不拉闸
参考答案:C
Han Li has _______ San Francisco in the USA many times?[ ]
A. been to
B. gone to
C. went to
D. been in
轴承在运转时主要有几种典型不正常现象?分别是什么?