单项选择题
Dry chemical extinguishers extinguish class B fires to the greatest extent by（）.
A.cooling B.smothering C.oxygen dilution D.breaking the chain reaction
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（）.
单项选择题 Control of flooding should be addressed（）.
