单项选择题
A.change from blue to orange
B.‘flare up’ and remain lighted
C.probably go out
D.stay blue
单项选择题 Before charging a refrigeration unit, the refrigerant charging lines should be（）
单项选择题 In the presence of an open flame or hot surfaces, chlorinated fluorocarbon refrigerants decomposes and from （）.
单项选择题 In an operating refrigeration system low on refrigerant, a liquid line sight glass will（）