Growth of trade will depend greatly on availability of energy sources. There may still be a trillion barrels of recoverable oil in the Middle East. But the oil crisis of 1974 has ____1____to renewed interest in coal and to a search for____2____ sources of energy. Solar, geothermal, and nuclear energy will play a large role in the years to come.

  Solar energy is available in ____3____ forms. Buildings can be heated and cooled by direct use of solar radiation, crops and trees, which are the most efficient converters of sunlight into energy, can be grown for their energy potential, wastes can be burned as ____4____, sunlight can be converted into DC (direct current) electricity, electric power can be____5____from the sun-warmed surface waters of the ocean, and lastly, solar radiation can be converted into heat that will drive electric power generators. Serious problems still remain as to ____6____and storage of solar energy.

  Geothermal energy is the energy contained within the earth. Heat is abundantly available deep in the earth's core and is constantly being produced. However, this heat is usually located at too deep a level for ____7____exploitation. In short, very little is known on the use of geothermal energy, and it has____8____been exploited.

  Nuclear energy is produced in nuclear power plants. At these plants atoms of uranium are split, thus ____9____masses of energy. Another source of energy under development is the nuclear fusion of certain atoms of hydrogen. This could eventually ____10____natural gas as a source of energy.
  A. rarely B. transformation C. fuel D. replace
  E. led F. alternative G. commercial H. briefly
  I. derived J. various K. relieving L. releasing
  M. transportation N. financial O. described
  I. E 2. F 3. J 4. C 5. I 6. M 7. G 8. A 9. L 10. D
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