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單項(xiàng)選擇題

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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單項(xiàng)選擇題

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

單項(xiàng)選擇題

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）

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