单选题
To get some idea of the amount of heat the sun gives off, think about this. If you could collect all the heat that hits the earth in a two-week period, it would equal the amount of all other known sources and reserves of energy: Wood, coal and oil. But even these sources of energy depend on the sun for their formation. For example, a tree would certainly never grow and provide fuel in the form of wood were it not for the sun. Because the sun is so important in the production of all forms of heating fuel, more and more time and money are being spent studying ways to change power from the sun directly into a form of heat. The process currently in use for collecting energy from the sun--known as solar energy--is quite simple. The sunlight hits a metal plate known as a flat-plate collector and the plate absorbs the heat front the sun. This heat, in turn, heats a liquid inside the plate. A layer of fiber-glass inside the plate helps prevent this heat from escaping. In this way, solar heat can be stored in a liquid solution equalling about 1,000 watts of electricity per square meter. In the 1960s, a solar furnace was installed in the Pyreness Mountains of France to test the use of solar energy. In this furnace, a mirror is used to concentrate the sun's heat. This concentrated heat keeps temperature in the furnace as high as 6,000 °F.
单选题
How does the amount of heat the sun gives off in two weeks compare with all other known sources and reserves of energy?