当基本闭塞设备不能使用时，应根据车站值班员的命令采用电话闭塞法行车。
参考答案：错
Convection spreads a fire by（）.
A.heated gases flowing through ventilation syetem
B.the transfer of heat across an unobstructed space
C.burning liquids flowing into another space
D.transmitting the heat of a fire through the ships metal
