单项选择题
Insufficient refrigerant in a refrigeration plant may result in （）.
A.high discharge pressure B.frosting of the crankcase C.high temperature of the overboard water D.low suction pressure of compressor
单项选择题 Air that may enter a refrigeration plant tends to collect in the （）.
单项选择题 Moisture should be kept out of an R-12 system because it tends to cause （）.
单项选择题 Black smoke coming from a boiler can be caused by （）.
