单项选择题

The internal part of the boiler, if found （）, has to be chemically washed by yard.

A.deformed
B.rusted
C.cracked
D.scaled

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单项选择题

Centrifugal pumps can be designed with a number of impellers （） to attain a high final delivery pressure.

A.in series
B.in parallel
C.either A or B
D.None of the above is tree

单项选择题

Which of the following pumps are self-priming, and can deal with liquid from a level below the pump: （）
(1)reciprocating
(2)vane
(3)gear

A.（1）only
B.（1）and（2）
C.（2）and（3）
D.（1），（2）and（3）

单项选择题

Which of the following will be the advantage of a centrifugal pump as compared with a reciprocating pump?（）
(1) Its discharge is continuous
(2) It has no internal valves
(3) Upon accidental closing of discharge valve, excessive pressure will not build up

A.（1），（2）
B.（2），（3）
C.（1），（2），（3）
D.（2）only