2. 外语
  3. Recently scientists have been【1】and perfecting other sources of energy: nuclear or atomic power, solar(sun)power, and synthetic(

Recently scientists have been【1】and perfecting other sources of energy: nuclear or atomic power, solar(sun)power, and synthetic(

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问题     Recently scientists have been【1】and perfecting other sources of energy: nuclear or atomic power, solar(sun)power, and synthetic(manmade)fuels. Nuclear power can offer some【2】, but fear of contamination【3】its use. The Three Mile Island【4】in Pennsylvania in 1979, when atomic waste material escaped【5】atmosphere, limited power plant construction【6】.【7】, scientists are doing research to discover other sources of fuel.【8】, some scientists have added alcohol to gasoline to conserve fuel.【9】, this research is still in the developmental【10】.
    The sun, from which nearly all energy【11】, is another solution【12】the energy crisis. Solar power is growing rapidly in popularity. All other fuels will【13】out after a period of years; the sun’s power is limitless.【14】burning any fuel—oil, coal, or wood—causes pollution, solar energy does not.【15】, no nation on earth has a corner【16】the solar market;【17】, no country has control【18】the sun. Although solar energy is increasing in popularity, it is still impractical and very expensive, and【19】not widely used.
    One immediate and viable(practical)solution, to the problem is conservation. We now have federal regulations【20】the winter temperature in public buildings to 65 degrees.
【17】
选项 A、what it is
B、for example
C、that is
D、in general
答案C
解析 that is意为“即，就是说，更确切地说”，是对前面作进一步的解释。
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