单项选择题
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
Dress up the （）.A.keywayB.shaftC.valveD.casing
单项选择题Dress up the （）.
A mixed-flow pump is a （） pump classified by the workin...
单项选择题A mixed-flow pump is a （） pump classified by the working principle.
A.self priming B.positive displacement C.reciprocating D.impeller
