[单项选择]People often speak of fire as though it were a living creature--It grows, dances, needs oxygen, feeds on whatever it can find, and then dies. And when a forest fire rages out of control, threatening human lives and homes, it must be fought like a "wild animal." The fight is often desperate, since firefighters’ best efforts may be dwarfed by the fury of a large fire. But the fire’s own traits can be used against it.
The heated air above a fire rises in a pillar of smoke and burnt gases, pulling fresh air in from the sides to replace it. Firefighters use this fact when they "fight fire with fire." They start a fire well in front of the one which they are fighting. Instead of traveling on in front of the huge fire, the smaller fire is pulled back toward it by the updrafts of the larger blaze. As it travels back to meet the large fire, the smaller backfire burns away the fuel that the forest fire needs to survive.
Even when a backfire has been well set, however, the fire may stil
A. faster than a horse can run
B. in all directions at the same speed
C. in whatever direction the wind is blowing
D. toward the nearest source of fuel