__________ are used to extinguish electrical fires.

听力原文： To extinguish different kinds of fires, several types of fire extinguishers have been invented. They must be ready for immediate use when fire breaks out. Most portable 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 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. If the heat is reduced by cooling the material below a certain temperature, the fire goes out. 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.

Another method of extinguishing fire is by cutting off the oxygen. This is usually done by covering the fire with sand, steam or some other things. A blanket may be used to cover a small fire.

A third method is called separation, which includes removing the fuel, or material easy to burn, from a fire, so that it can find no fuel.

The method that is used to put out a fire depends upon the type of fire. Fires have been grouped in three classes. Fires in wood, paper, cloth and the like are called Class A fires. These materials usually help keep the fire on. Such fires can be stopped most readily by cooling with water.

(30)

A．Separating the fire.

B．Reducing the heat.

C．Removing the fuel

D．Cutting off the oxygen.

A.deprival of oxygen

B.a water spray

C.soda-acid

D.foam

What techniques are used in this extended definition: A patent is a form of intellectual property. A patent gives its owner the right to exclude others from making, using, selling, and importing an invention for a limited period of time, usually twenty years. The patent rights are granted in exchange for an enabling public disclosure of the invention. In most countries, patent rights fall under civil law and the patent holder needs to sue someone infringing the patent in order to enforce his or her rights. In some industries patents are an essential form of competitive advantage; in others they are irrelevant.

A、comparison/contrast

B、further explanation

C、example

D、classification

Oil fires are best extinguished by ______.

A.cutting off the supply of oxygen

B.removing the fuel

C.cooling below the ignition temperature

D.spraying with water