82.
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. 这题为什么选C呢? 我不太明白段落的意思,我自己的理解为尽管技术改进和设备成本减少使得solar power是合算的,但是其经济可行性没有改变,还是$35.而所谓的经济可行性是每桶石油的价格必须提升,以使得新的solar power工厂比新的oil-fired power工厂更为实惠. 答案的思路是说尽管石油的价格提升了,但是石油工厂的效率也提高了,所以其用油就省了,所以solar power就不经济可行了吗?请NN们指教~~~ | 
