活塞式气压机一般性能参数包括哪些？
参考答案：
流量、压力、缸径、转速、冲程
She reached the top of the hill and stopped _______ on a big rock by the side of the path. [ ]
A. to have rested
B. resting
C. to rest
D. rest
目前国内地下矿山普遍使用（）电机车。
A.直流
B.交流
C.蓄电池
