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單項選擇題

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

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單項選擇題

Dress up the （）.

A.keyway
B.shaft
C.valve
D.casing

單項選擇題

A mixed-flow pump is a （） pump classified by the working principle.

A.self priming
B.positive displacement
C.reciprocating
D.impeller