柴油泵的油压依靠()来调节。
A.进口阀
B.出口阀
C.旁通或溢流阀
D.以上三种方法均可使用
参考答案:D
They didn't leave the station ___ they got on the train. [ ]
A. until
B. by
C. after
D. at
JL474Q气缸工作面应耐高温、耐腐蚀、()
A、光滑
B、清洁
C、耐磨损