单项选择题
A.keyway B.shaft C.packing D.valve
Which pump is the self-priming pump?（）A.turbineB.centri...
单项选择题Which pump is the self-priming pump?（）
A.turbine B.centrifugal C.ejector D.mixed flow
The younger motorman as well as the others （） to operat...
单项选择题The younger motorman as well as the others （） to operate the oil separator.
A.has learnt B.have learnt C.learn D.are learning
A water pump can not supply water after startingIt may ...
单项选择题A water pump can not supply water after startingIt may be caused by （）.
A.closed discharge valve B.broken pipe line C.worn shaft D.both A and B
