求解新PREP CR2 82

zhangfn07

82.   (33511-!-item-!-188;#058&007598)

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A为什么不对呢？

zxppx

请注意括号里面的解释 (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），石油价格的变化是为了改变solar power plants和oil-fired power plants之间的效率之比。
C选项正好说明，oil-fired power plants的效率在科技进步的情况下得到了提高（即使题干第一句话已经提到solar power plants的效率已经提高），所以两者之间的效率比可能仍然保持不变，因此threshold is unchanged.
A选项，虽然提到石油成本下降，但是不能代表就一定能改变两者之间的效率，因为括号中用的是in order for, 也可能其他因素也会影响。比如，C选项就能很好解释A的漏洞，即使Oil价格下降了很多，但是如果oil-fired power plants比solar power plants更加有效，那么实际上threshold将会上升，而不是下降。这样的话，oil就比solar power更加经济