单项选择题
Before using a fixed CO2 system to fight an engine room fire，you must（）.
A.secure the engine room ventilation B.secure the machinery in the engine room C.evacuate all engine room personnel D.All of the above
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（）.
单项选择题 Automatic fire dampers in ventilation systems are operated by use of（）.
