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.
76. How much energy given off by the sun reaches the earth?
A. 100% but indirectly. B. 5%.
C. 50%. D. only a very tiny amount.
77. The reason why all the solar energy falling on the earth can't be utilized is that ______.
only a very small part is available the sun is too distant from the earth
it takes thousands of years for this energy to be stored up in coal and oil
our scientific knowledge is not sufficient
78. Which of the following statements is NOT true?
Even windmill's action depends on the sun.
The sun produces enormous energy for man to make use of.
Some day man will be able to utilize 100% of the solar energy that gets to the earth.
The sun produces different heating effects in different places.
79. In order to support this argument, the writer gives the example that _______.
a machine using solar energy efficiently has already been developed
the sun is our final source of power
man uses only a tiny part of the sun's energy
the part of the sun's energy we use is used indirectly
80. This passage centers mainly on ________.
harnessing energy through chemistry
our last source of power
how water power is produced
the amount of solar energy that can be utilized
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