单项选择题
Halon fire extinguishers are NOT effective when used on which types of fires?（）
A.Fires in electrical equipment B.Flammable oils and greases C.Class A fires in ordinary combustibles D.Materials containing their own oxygen
单项选择题 Halon extinguishes fire primarily by（）.
单项选择题 Halon extinguishes a fire by（）.
单项选择题 Halon extinguishers used on a class C fire should be directed at the（）.
