If the sun has enough【C1】______to warm and light the whole earth, it must have enough power to do other things,【C2】______. Can we use the sun's【C3】______energy to supply electricity, or at least to perform. the function which electricity or other types of power usually perform？ The answer is【C4】______.
For example, people have for many years been using the【C5】______heat of the sun to cook by solar【C6】______which have been built with several incurred【C7】______reflecting the sun and focusing the heat on the cooking element. This【C8】______can be used like a gas or electric stove; it is more expensive to make but it doesn't need any【C9】______and so costs【C10】______to use. Another【C11】______of using solar energy is in house heating.
The【C12】______of energy we use most is electricity, and every day more is【C13】______. But electricity has to be made too, and to make it huge quantities of fuel is required -- oil, coal, gas and nowadays even uranium.
The question which【C14】______everyone today is: how long will these fuels【C15】______？ Nobody knows it for sure,【C16】______most experts think it will soon be difficult to obtain sufficient electricity from these sources. It is possible that the sun can make a(n)【C17】______here, too.
Solar power has already been used to produce【C18】______heat. In Southern France a solar furnace has been built,【C19】______temperatures reach more than 3 000 centigrade. This furnace is not only used for experiment【C20】______, but could be used to produce steam for a power station.
【C1】

A. power
B. time
C. heat
D. temperature