新prep2-82，帮帮忙啊！

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.

正确答案是C

题目就看得云里雾里的了，特别是划线部分，逻辑关系理不清

哪位NN帮忙解释说明下~~谢谢

这道题确实关键在于对题目的理解。其实就是将单位太阳能以石油为基础进行经济性对比，比如一桶油价格为X能产生N千瓦的电力，那么要让太阳能比石油经济只要确认用太阳能产生N千瓦的电力所需要的成本低于X就可以了。

题目中提到的是随着技术提升成本X的太阳能能够产生N+M千瓦的电力，为什么对应的阈值没有变。这样理解就很简单，因为随着火力发电厂的进步X的石油也能产生N+M千瓦的电力。归根到底这里是一种相对比较而不是绝对的，两者进步一样快的话那么那个阈值就一直不会下来。

我理解这个句子是：每桶油的价格必须上涨35元，才能使新太阳能工厂比新石油能源工厂更经济。

我想的是如每桶油的价格和太阳能的生产无关，只影响到石油工厂， 所以油价上涨就是说石油工厂生产成本提高。只有当生产成本提高的某程度的时候，才和太阳能生产成本持平。

所以我很困惑，我选了A: The cost of oil has fallen dramatically.我想的是就算技术不变，如果石油工厂成本一直再减，就算太阳能技术提高了，35元的差价还是可以保持啊……

虽然我能理解C也对……请帮忙解答！！！谢谢！！

A错了。因为如果是油价降了的话，那个每桶油需上涨的钱就不是UNCHANGED 了，就是提高了。所以它一旦是UNCHANGE 就说明相对价格是不变的，所以油价就不可能下降了。