液压系统保证有足够高的压力以避免（）
A、液压油出现渗漏
B、系统失去压力
C、泵产生气穴
参考答案：C
— He's seldom stopped from smoking, _____?
— _____. The doctor often warns him not to. [ ]
A. isn't he, Yes
B. is he, Yes
C. isn't he, No
D. is he, No
2M速率以下电路调到备用的时限为（）分钟（从维护人员到达机房算起）。
A.5
B.3
C.10
D.20
