If you made a list of all the jobs performed by the different kinds of energy, you would fill many pages. Nuclear energy is used in some areas of the United States. But there are dangers. Waste materials from nuclear (51) would destroy life if they leaked (52) the land. When nuclear energy is produced, a lot of (53) is produced, too, so a flow of lake or ocean water is used to cool the operations. Then the water (54) to its source. If the returning water were too hot, it would destroy fish and other (55) . Cow manure is being used to produce a kind of (56) . The manure from farms is put into a machine to convert it to a liquid. Then the gas is formed (57) a natural process. If the converter were not so (58) at the present time, it would be used in many places to provide (59) . Garbage has become an energy source. It (60) to oil, steam, or electricity, or it is used on the land. But recent (61) about power supplies has led to increased interest in the use of wind (62) a source of electrical power. Windmills are clean and they (63) no waste. And they use a (64) resource. Some scientists consider that wind energy systems can fulfill a valuable (65) in meeting the energy needs of industrialized nations and of the developing world.

A. high temperature
B. hot air
C. heat
D. warmth