单项选择题
CO2 extinguishes a fire by（）.
A.cooling B.smothering C.chemical action D.All of the above
单项选择题 Cargo transfer operations on a tanker need NOT be stopped when（）.
单项选择题 Blocking open or removing fire dampers can cause（）.
单项选择题 Before using a fixed CO2 system to fight an engine room fire，you must（）.
