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. 这题就没看懂，the threshold of economic viability的概念也没搞清楚，哪位给解释一下。作者: NicoleYu 时间: 2010-3-17 12:10
threshold of economic viability 我理解是说经济上可行的临界值
后面括号里面的内容就是对这个进行解释，不过因为句子比较长（有点语法题的感觉），所以可能影响判断
首先我们明确这其中比较的是solar power 和oil-fired power：文章中说的这个$35就是这两者经济可行性临界值的差价。打个比方，如果oil-fired power的这个临界值是$100 per barrel，那么solar power就是$135 per barrel（也就是说经济上solar power不及oil-fired power划算）。
文章说solar power技术进步等就是要说明solar power的这个临界值降低了，变得成本更低更有经济竞争力了，但是二者的差值仍是35，证明oil-fired power的临界值也降低了，也变得更经济了，所以要在选项中的寻找的解释项就是要说明是什么让oil-fired power变得更经济了。C选项说技术改变使oil-fired power plants效率提高了，就提出能解释这个现象的原因，所以选C
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