单项选择题
If there has been a fire in a closed unventilated compartment it may be unsafe to enter because of （）.
A.unburned carbon particles B.excess nitrogen C.a lack of oxygen D.excess hydrogen
单项选择题 After a fire has been extinguished in a closed space, personnel may safely enter the space when （）.
单项选择题 Which of the petroleum products listed has the lowest flash point?（）
单项选择题 Which of the listed fire extinguishers is recommended for use on an electrical switchboard fire?（）
