單項(xiàng)選擇題

Black smoke coming from a boiler can be caused by （）.

A.low water level
B.low oil pressure
C.excessively high fuel pressure
D.an improper air/fuel ratio

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單項(xiàng)選擇題

Which of the following pumps belongs to centrifugal pump?（）

A.Reciprocating pump
B.Screw pump
C.Diffuser pump
D.Water-ring pump

單項(xiàng)選擇題

The advantage of a centrifugal pump as compared with a reciprocating pump is that （）.

A.discharge is continuous
B.it has no internal valves
C.upon accidental closing of discharge valve, excessive pressure will not build up
D.all of the above are true