带油压顶杆卸载装置的活塞式制冷压缩机顶杆伸出一半,导致吸气阀片敲击有可能是因为:().
A.油压太高
B.油压不足
C.A.B都不可能
D.A或B
参考答案:B
下列实验操作正确的是[ ]
A.干燥氧气
B.测定溶液pH
C.量取9.0mL液体
D.向试管中滴加液体
Our class ____ more than 50 students. [ ]
A. builds of
B. is made up
C. consists of
D. is consisted of