单项选择题
Dry chemical fire extinguishers are effective on which type(s) of fire?（）
A.Burning oil B.Electrical C.Paint D.All of the above
单项选择题 Dry chemical extinguishers extinguish class B fires to the greatest extent by（）.
单项选择题 Convection spreads a fire by（）.
单项选择题 Controls for a fixed carbon dioxide system shall be mounted（）.
