绞车使用全封闭，风扇自冷式隔爆鼠笼型异步电动机的调速性能（）。
A、好
B、差
C、一般
参考答案：B
My lecture is only two weeks away. _____ has come for me _____ it. [ ]
A. Time; to prepare
B. The time ; to prepare
C. Time; to prepare for
D. The time ;to prepare for
简述留置权的概念和成立条件。
