排水泵房宜设计成自灌式，且在吸水管上应设有( )，以满足水泵检修的需要。
A．止回阀
B．闸阀
C．观测孔
D．真空表
参考答案：B
These books ________ well, and they will _______ soon. [ ]
A. sell; sell out
B. are sold; sell out
C. sell; be sold out
D. are sold; sold out
协定关税
