离心水泵在填料箱或水管法兰处进气，都会导致水泵抽不上水。
参考答案：对
Tom is in the _______. He is playing ping-pong,[ ]
A. classroom
B. gym
C. library
They had an accident on the road and didn’t ________ at their hotel until after midnight.
A．check out
B．check in
C．check on
D．check over
