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
单项选择题 The presence of bubbles in a refrigeration system liquid line may （）.
单项选择题 Air entering an air-cooled refrigeration system is indicated by （）.
单项选择题 When installing a hydraulic hose, which of the following precautions should be taken?（）
