单项选择题
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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相关考题
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单项选择题
Which of the following pumps belongs to centrifugal pump?（）
A.Reciprocating pump
B.Screw pump
C.Diffuser pump
D.Water-ring pump -
单项选择题
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 -
单项选择题
A pump is said to have "negative suction head" when the pump is located （）.
A.between the suction and discharge
B.below the liquid supply
C.above the liquid supply
D.any of the above
