根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。 To extinguish (熄灭) different kinds of fires, several types of fire extinguishers have been invented.__71__ Most portable (手提式的) kinds operate for less than a minute, so they are useful only on small fires. The law requires ships, trains, buses and planes to carry extinguishers. Since fuel, oxygen (氧气) and heat must be present in order for fire to exist, one or more of these things must be removed or reduced to extinguish a fire.__72__ The cooling method is the most common way to put out a fire.Water is the best cooling material because it is low in cost and easy to get. __73__ This is usually done by covering the fire with sand, steam or some other things. A blanket may be used do cover a small fire. A third method is called separation.__74__ The method that is used to put out a fire depends upon the type of fire. Fires have been grouped in three classes.__75__ These materials usually help keep the fire on. Such fires can be stopped most readily by cooling with water.
F．If the heat is reduced by cooling the material below a certain temperature, the fire goes out. G．It includes removing the fuel, or material easy to burn, from a fire, so that it can find no fuel. |