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  3. The energy which the sun radiates goes in every direction, and only a minute part of it falls on the earth. Even so, it represen

The energy which the sun radiates goes in every direction, and only a minute part of it falls on the earth. Even so, it represen

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问题     The energy which the sun radiates goes in every direction, and only a minute part of it falls on the earth. Even so, it represents power of about 5, 000, 000 horsepower(马力)per square mile per day: the sun gives us as much energy every miunte as mankind utilizes in a year. At present, we use this energy indirectly, and it is our final source of power. Coal represents the chemical action of the sun on green plants thousands of years ago. Water power results from the rain formed by vapor which comes from the evaporation of water under the sunshine. Even windmills operate because of air currents set in motion by the different heating affects of the sun in different places. Some day, through chemistry or some type of solar engine, we shall harness this great source of energy more directly. Already a scientist has worked out an engine, surprisingly efficient, in which the sun’s rays are concentrated through mirrors on a tube of water to create steam.
This passage centers mainly on______.
选项 A、harnessing energy through chemistry
B、our last source of power
C、how water power is produced
D、the amount of solar energy that can be utilized
答案D
解析 文章主旨题，本文主要说明人们如何尽可能充分利用太阳能。
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