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  3. "Geothermal Energy" Geothermal energy is natural heat from the interior of the Earth that is converted to heat buildings and

"Geothermal Energy" Geothermal energy is natural heat from the interior of the Earth that is converted to heat buildings and

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问题 "Geothermal Energy"
   Geothermal energy is natural heat from the interior of the Earth that is converted to heat buildings and generate electricity. The idea of harnessing Earth’s internal heat is not new. As early as 1904, geothermal power was used in Italy. Today, Earth’s natural internal heat is being used to generate electricity in 21 countries, including Russia, Japan, New Zealand, Iceland, Mexico, Ethiopia, Guatemala, El Salvador, the Philippines, and the United States. Total worldwide production is approaching 9,000 MW (equivalent to nine large modern coal-burning or nuclear power plants)—double the amount in 1980. Some 40 million people today receive their electricity from geothermal energy at a cost competitive with that of other energy sources. In El Salvador, geothermal energy is supplying 30% of the total electric energy used. However, at the global level, geothermal energy supplies less than 0.15% of the total energy supply.
   Geothermal energy may be considered a nonrenewable energy source when rates of extraction are greater than rates of natural replenishment. However, geothermal energy has its origin in the natural heat production within Earth, and only a small fraction of the vast total resource base is being utilized today. Although most geothermal energy production involves the tapping of high heat sources, people are also using the low-temperature geothermal energy of groundwater in some applications.
   Geothermal Systems
   A   The average heat flow from the interior of the Earth is very low, about 0.06 W/m2. B   This amount is trivial compared with the 177 W/m2 from solar heat at the surface in the United States. However, in some areas, heat flow is sufficiently high to be useful for producing energy For the most part, areas of high heat flow are associated with plate tectonic boundaries. Oceanic ridge systems (divergent plate boundaries) and areas where mountains are being uplifted and volcanic island arcs are forming (convergent plate boundaries) are areas where this natural heat flow is anomalously high.    C
   On the basis of geological criteria, several types of hot geothermal systems (with temperatures greater than about 80°C, or 176°F) have been defined, and the resource base is larger than that of fossil fuels and nuclear energy combined. A common system for energy development is hydrothermal convection, characterized by the circulation of steam and/or hot water that transfers heat from depths to the surface.   D
   Geothermal Energy and the Environment
   The environmental impact of geothermal energy may not be as extensive as that of other sources of energy. When geothermal energy is developed at a particular site, environmental problems include on-site noise, emissions of gas, and disturbance of the land at drilling sites, disposal sites, roads and pipelines, and power plants. Development of geothermal energy does not require large-scale transportation of raw materials or refining of chemicals, as development of fossil fuels does. Furthermore, geothermal energy does not produce the atmospheric pollutants associated with burning fossil fuels or the radioactive waste associated with nuclear energy. However, geothermal development often does produce considerable thermal pollution from hot waste-waters, which may be saline or highly corrosive.
   Geothermal power is not always popular. For instance, geothermal energy has been produced for years on the island of Hawaii, where active volcanic processes provide abundant near-surface heat. There is controversy, however, over further exploration and development. Native Hawaiians and others have argued that the exploration and development of geothermal energy degrade the tropical forest as developers construct roads, build facilities, and drill wells. In addition, religious and cultural issues in Hawaii relate to the use of geothermal energy. For example, some people are offended by using the "breath and water of Pele" (the volcano goddess) to make electricity. This issue points out the importance of being sensitive to the values and cultures of people where development is planned.
   Future of Geothermal Energy
   At present, the United States produces only 2800 MN of geothermal energy. However, if developed, known geothermal resources in the United States could produce about 20,000 MW which is about 10% of the electricity needed for the western states. Geohydrothermal resources not yet discovered could conservatively provide four times that amount (approximately 10% of total U.S. electric capacity), about equivalent to the electricity produced from water power today.
Look at the four squares [■] that show where the following sentence could be inserted in the passage.
   One such region is located in the western United States, where recent tectonic and volcanic activity has occurred.
   Where could the sentence best be added?
   Click on a square [■] to insert the sentence in the passage.
选项 A、 
B、 
C、 
D、 
答案C
解析 Vocabulary reference is a transitional device that connects the insert sentence with the previous sentence. "One such region" is a phrase in the insert sentence that refers to "Oceanic ridge systems" in the previous sentence.
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