汽轮机纯冲动级的最佳速比为（）
A.1/2；
B.1/4；
C.3/4；
D.都不是。
参考答案：A
— Alice, why aren't you at work today?
— I _____ a day off. [ ]
A. have given
B. have been given
C. gave
D. was given
160km/h区段接触网的拉出值限界值为（）。
A、400mm
B、450mm
C、475mm
D、500mm
