Technological improverments and reduced equipment costs made converting solar energy directly into electricity far more cose-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 ecnomical 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 eco- nomic viability? A The cost of oil has fallen dramatically. B The reduction in the cost of solar-power equipment has occured despite increased raw material costs for that equipment. C Technolofical changes have increased the efficiency of oil-fired power plants. 答案C, 请问，括号里面那句，怎么翻译？谢谢了 | 
