45号钢属于（）钢。
A.低碳
B.中碳
C.高碳
D.合金钢
参考答案：B
No _____ that you will pass the coming exam, for you have been well prepared for it. [ ]
A. wonder
B. problem
C. question
D. doubt
简述主控系统与变流系统间的接线,并描述其功能.
