离心泵运行时,出现泄漏严重的可能原因是().
A.填料压盖压偏
B.密封环磨损严重
C.密封液压力不当
D.以上原因都可能
参考答案:D
Everyone in our class was working hard and doing what we could _______ a good college.
A.enter。m
B.to enter
C.entering。m
D.entered
下列哪些与经济周期有关()。
A.失业率
B.通货膨胀率
C.股票市场
D.总需求与总供给的均衡