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  3. The exploitation of the power in the Sun’s rays is a form of alternative energy now showing new commercial promise. In the

The exploitation of the power in the Sun’s rays is a form of alternative energy now showing new commercial promise. In the

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问题      The exploitation of the power in the Sun’s rays is a form of alternative energy now showing new commercial promise.
     In the US, manufacturers have made important 【C1】______ in the development of the technology to bring down the cost of solar conversion systems 【C2】______ improving their reliability.
     The direct conversion of solar 【C3】______ electrical energy, using photovoltaic cells 【C4】______ distinct advantages as an alternative energy option.
     【C5】______ other forms of renewable energy, photovoltaic is based on modular solid state devices which can be mass 【C6】______ at a relatively low cost.
     Here wafers of silicon—not dissimilar 【C7】______ ones which are turned into silicon chips— 【C8】______ an electric current when light falls upon them.
     When built into panels or modules where each cell interconnects, the amount of electricity generated can be large enough to 【C9】______ a home or even a community.
     Over the past 10 years, 【C10】______ extensive research and substantial Government and private industry funding, the price of photovoltaic modules has dropped 【C11】______ .
    【C12】______ in 1973-74 the price per peak watt was between US $100 and $150, commercial prices for small array system now vary between $6.50 and $7 per watt.
     This rapid price reduction has been accompanied by a 400 per cent jump in the 【C13】______ efficiency of photovoltaic modules.
     【C14】______ solar cells are poor converters of sunlight to electricity. Early cells could only manage to mm about five per cent of the incident rays into electricity, but recent development have increased 【C15】______ to more than 10 percent.  
【C12】
选项 A、Now that
B、Provided
C、Although
D、Whereas
答案D
解析 whereas意为“而……”，从上下文判断后句为前句的对比。
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