单项选择题
A.sealed B.cracked C.shape changed D.deformed
The internal part of the boiler, if found （）, has to be...
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
Centrifugal pumps can be designed with a number of impe...
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
Which of the following pumps are self-priming, and can ...
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）
