单项选择题

Dirt should not be allowed to contaminate a grease lubricant because the （）.

A.dirt will cause corrosion of bearing
B.bearings will leak oil excessively
C.dirt is very abrasive when mixed with grease
D.grease will become inflammable

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单项选择题

The presence of bubbles in a refrigeration system liquid line may （）.

A.promote refrigerant dehydration
B.be absorbed in the receiver
C.cause low condensing pressure
D.carry moisture and lead to corrosion

单项选择题

Air entering an air-cooled refrigeration system is indicated by （）.

A.frosting of the liquid line
B.higher than normal head pressure
C.a clear sight glass
D.abnormally cold reefer boxes

单项选择题

When installing a hydraulic hose, which of the following precautions should be taken?（）

A.The hose should not be twisted
B.The hose should be protected with a sleeve if it is subjected to rubbing
C.There should be some slack in the hose
D.All of the above