单项选择题
In a refrigeration plant the （） need defrosting.
A.fan B.compressor C.condenser D.evaporator
单项选择题 Hot gas defrosting uses the hot gas from （） to defrost the evaporator.
单项选择题 The evaporating pressure in R22 vapor compression refrigeration plant should be （） atmospheric.
单项选择题 The primary task of the compressed air system is to deliver the starting air necessary for （）
