When subjected to high heat from a open flame, or an electric heating element, which of the listed refrigerants will break down and produce phosgene gas?（）

A.Suction head
B.Pump head
C.Discharge head
D.Total head

A.toxic
B.flammable
C.explosive
D.all of the above

A.Fire pump and lube oil pump
B.Lube oil pump and distilling plant
C.Distilling plant and shaft alley door
D.Shaft alley door and fixed CO2 release