2. 外语
  3. Recently scientists have been【C1】______and perfecting other sources of energy: nuclear or atomic power, solar(sun)power, and syn

Recently scientists have been【C1】______and perfecting other sources of energy: nuclear or atomic power, solar(sun)power, and syn

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问题     Recently scientists have been【C1】______and perfecting other sources of energy: nuclear or atomic power, solar(sun)power, and synthetic(manmade)fuels. Nuclear power can offer some【C2】______, but fear of contamination【C3】______its use. The Three Mile Island【C4】______in Pennsylvania in 1979, when atomic waste material escaped【C5】______atmosphere, limited power plant construction【C6】______.【C7】______, scientists are doing research to discover other sources of fuel.【C8】______, some scientists have added alcohol to gasoline to conserve fuel.【C9】______, this research is still in the developmental【C10】______.
    The sun, from which nearly all energy【C11】______, is another solution【C12】______the energy crisis. Solar power is growing rapidly in popularity. All other fuels will【C13】______out after a period of years; the sun’s power is limitless.【C14】______burning any fuel—oil, coal, or wood—causes pollution, solar energy does not.【C15】______, no nation on earth has a corner【C16】______the solar market;【C17】______, no country has control【C18】______the sun. Although solar energy is increasing in popularity, it is still impractical and very expensive, and【C19】______not widely used.
    One immediate and viable(practical)solution, to the problem is conservation. We now have federal regulations【C20】______the winter temperature in public buildings to 65 degrees."
【C19】
选项 A、furthermore
B、ever since
C、therefore
D、then
答案C
解析 前后为因果关系，所以用therefore。
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