GMAT申友逻辑CR题库-Technological improvements and reduced equipment costs have made converting solar energy directly into electricity far more cost-efficient in the last-破解版08-真题答案解析

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CR67-77题

Technological improvements and reduced equipment costs have made converting solar

energy directly into electricity far more cost-efficient in the last decade. However, the threshold of economic viability for solar power (that is, the price per barrel to which oil would have to rise in order for new solar power plants to be more economical than new oil-fired power plants) is unchanged at thirty-five dollars.

Which of the following, if true, does most to help explain why the increased cost-efficiency of solar power has not decreased its threshold of economic viability?

A. The cost of oil has fallen dramatically.

B. The reduction in the cost of solar-power equipment has occurred despite increased raw material costs for that equipment.

C. Technological changes have increased the efficiency of oil-fired power plants.

D. Most electricity is generated by coal-fired or nuclear, rather than oil-fired, power plants.

E. When the price of oil increases, reserves of oil not previously worth exploiting become economically viable.

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讨论了太阳能和火力两种发电方法:

(1) ：太阳能发电的成本=将太阳能转化为电能的成本

(2)：火力发电的成本=石油的成本+将石油转化为电能的成本这两个公式的区别在于：太阳能是不要钱的，而石油要钱。而当石油的成本=临界点(threshold)的时候， (1) = (2) 即：太阳能转化成电能的成本= threshold+将石油转化成电能的成本由此得到：(3) threshold= 太阳能转化成电能的成本 - 将石油转化成电能的成本所以，threshold只是两种发电成本的差，是由两种发电的成本决定的，与实际的油价并没有关系。所以，A选项是无关选项。而题目中提到说，太阳能转化的效率提高（即成本下降），而threshold不变，那么从公式(3)中就很容易得到：是因为石油转化成电能的成本也降低了（即火力发电效率提高）。所以选C。