There are four factories in our institute, ____________.
A. with each has over 100 workers
B. each having over 100 workers
C. which there are over 100 workers
D. with having over 100 workers
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72. He left the room____.
A. with the door closing
B. with the door closed
C. with the door being closed
D. with the door being closed
在没有泄露的情况下，泵在单位时间内所输出的油液体积称为（ ）
A. 理论流量
B. 实际流量
C. 最小流量
D. 排量
泵的实际流量和理论流量之比称之为（）
A. 容积效率
B. 机械效率
C. 总效率
液压泵工作应该具备如下哪些条件？
A. 有一个或若干个密闭工作空间
B. 该密闭工作空间体积稳定不变
C. 该密闭工作空间能周期变化
D. 有与密闭空间相协调的配流装置
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