单项选择题
Blocking open or removing fire dampers can cause（）.
A.fixed foam systems to be ineffective B.faster cooling of the fire C.the accumulation of explosive gases D.the fire to spread through the ventilation system
单项选择题 Before using a fixed CO2 system to fight an engine room fire，you must（）.
单项选择题 Before a tank is to be crude oil washed，the oxygen content in the tank must be measured at a position（）.
单项选择题 Backfire flame arrestors are installed on（）.
