Prep08 CR2 第82题不懂 跪求高手解释！

sunspirit2011

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

Technologicalimprovements and reduced equipment costs have made converting solar energydirectly into electricity far more cost-efficient in the last decade.  However, the threshold of economic viabilityfor solar power (that is, the price per barrel to which oil would have to risein order for new solar power plants to be more economical than new oil-firedpower plants) is unchanged at thirty-five dollars.
Which of thefollowing, if true, does most to help explain why the increased cost-efficiencyof solar power has not decreased its threshold of economic viability?
A. The cost of oilhas fallen dramatically.
B. The reduction inthe cost of solar-power equipment has occurred despite increased raw materialcosts for that equipment.
C. Technologicalchanges have increased the efficiency of oil-fired power plants.
D. Most electricityis generated by coal-fired or nuclear, rather than oil-fired, power plants.
E. When the price of oilincreases, reserves of oil not previously worth exploiting become economicallyviable.

请问本题如何分析并选出正确答案？虽然看了Prep08CR2解释——技术的进步，使得太阳能转换为电能变得更加的经济， 但是使用可行性准入门槛依旧是35元。问为什么提高了成本效率，为什么没有减低门槛。Ｃ选项说技术的进步也改变了ｏｉｌ－ｆｉｒｅｄ公司的效率。注意括号里面的解释，括号里面的大致的意思是说太阳能和石油成正相关，如果石油技术进步，那么太阳能转换技术也进步了，所以总体比率不变，所以门槛还是没降低——但还是似懂非懂。我想关键是文中括号内的话没有理解。


请高手指导啊！万分感激！（答案是C）