单项选择题 Accumulations of oily rags should be（）.

单项选择题 A high-velocity fog stream can be used in fire fighting situations to drive heat and smoke ahead of the fire fighters in a passageway. This technique should only be used when（）.

单项选择题 A fire hose with a nozzle attached must be connected to each hydrant except when exposed to heavy weather or when the（）.