单项选择题
The oil in a cargo winch gear box should be sampled periodically to （）.
A.prevent the gear box from leaking
B.prevent the oil from becoming inflammable
C.make sure it has not become contaminated
D.make sure the motor bearings are lubricated
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A spur gear pump should be operated with the discharge valves （）.
A.slightly opened
B.throttled
C.fully opened
D.halfway opened -
单项选择题
The capacity of a centrifugal pump can be increased by the installation of a larger diameter impeller Another means of increasing the pump capacity is to （）.
A.increase speed
B.increase the size of the cardent assembly
C.reduce wearing ring clearances
D.change the pump to a "close coupled" arrangement -
单项选择题
Which of the following forms of energy is demonstrated through the process of combustion?（）
A.Chemical energy
B.Mechanical energy
C.Thermal energy
D.Electrical energy
