There are different ways in which people try to deal with the problem of energy. One way is greater production of common energy

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问题     There are different ways in which people try to deal with the problem of energy. One way is greater production of common energy sources(能源), such as coal, oil and gas. The trouble with these sources, however, is that they are not renewable.
    Another way is energy conservation(节能), which means using energy more efficiently. In some very cold countries people build special houses to save energy. They place materials between the inside and the outside of the walls of the house to keep the cold out and the warmth in. The house is heated by the lights, the body heat of people and the other equipment in it.
    Finally, renewable energy sources are used even though they are often expensive to develop. One form of these is geothermal energy. In certain parts of the world the temperature of the earth increases thirty degrees centigrade with each kilometer down. At six kilometers, therefore, it rises to nearly two hundred degrees. To get the heat, water is pumped(压, 抽)down into the rocks and back up to the surface. Heat from the earth is already used in certain countries.  
From the text we learn that coal

选项 A、is quite easy to produce
B、is used most efficiently
C、is one of the common energy sources
D、could be renewed only by new technology

答案C

解析 简单细节题。
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