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[Helr题库] 一道prep700+逻辑题:Technological improvements and reduced equipment costs have made c

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发表于 2019-5-10 11:15:25 | 显示全部楼层 |阅读模式

据说是700+水平的逻辑题。

解释:为啥太阳能发电成本降低了, 使用太阳能经济可行性的门槛没有变 ?

前提:太阳能经济可行性的门槛 == 油价P : cost (太阳发电) < cost(燃烧油发电)

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.

我看到网上有很多解释,甚至举出数字来理解, 但我依然没有看懂, 因为我无法因此排除A。

我自己的想法是:

极端想:   当达到某油价P1,      cost (太阳发电) = cost(燃烧油发电)       当油价超过P1,    cost (太阳发电) <  cost(燃烧油发电) ,  因此P1就是那个临界点。

这里面 the threshold of economic viability for solar power === the price per barrel to which oil would have to rise  相当于油价/桶 ==P1 ( 我觉得关键在于知道“the threshold of economic viability for solar power ”是啥。)

选项A :油价降低 ==P1降低 ==the threshold of economic viability for solar power 降低     但题目说”the threshold of economic viability for solar power “   " unchanged  "  不符合题目, 排除
选项B : 用太阳能成本降低  重复前提, 但没有解释结论, 排除
选项C : 燃烧油效率增加 ==每单位用油减少 === cost(燃烧油发电)减少    前提: cost (太阳发电) 减少, 选项C 表明cost(燃烧油发电)减少       因此 cost (太阳发电) = cost(燃烧油发电)   依然成立, 因此P1没有变,即“the threshold of economic viability for solar power ”没有变,  正确
选项D: 无关选项
选项E : 无关选项


我也不知道自己分析得对不对, 希望有大神过来指正。 也希望大家可以分享自己对这道题的理解, 互相学习。 (比如怎样比较AC, 排除A ,选择C)


发表于 2019-5-15 18:14:09 | 显示全部楼层
https://gmatclub.com/forum/technological-improvements-and-reduced-equipment-costs-have-made-conve-26675.html#p464694

GMATninja的意见:A:The actual cost of the oil doesn't change the threshold. Rather, the price of oil simply determines whether we are above, below, or at the threshold. For example, if the threshold is $35 per barrel and the cost of oil falls from $30 per barrel to $5 per barrel, that would take us further away from the threshold but would not CHANGE the threshold itself. Eliminate choice (A).


C:If the cost of converting solar energy into electricity goes DOWN, we would expect the threshold of economic viability to decrease. However, if the cost of converting oil into electricity goes down, we would expect the threshold to INCREASE. Thus, if the cost of converting solar AND the cost of converting oil BOTH decrease, the expected changes to the threshold could cancel each other out (one makes the threshold go up, the other makes the threshold go down, so the threshold could remain the same).


希望有帮助,感谢提出这题,我也学到了
 楼主| 发表于 2019-5-16 11:28:18 | 显示全部楼层
frankshu94 发表于 2019-5-15 18:14
https://gmatclub.com/forum/technological-improvements-and-reduced-equipment-costs-have-made-conve-26 ...

感谢回复。 但是 “GMATninja” 的解释说明了 选项A 是可以解释“he threshold of economic viability for solar power  is unchanged”   但是选项A不是正确答案。

发表于 2019-5-17 13:45:11 | 显示全部楼层
小目标750 发表于 2019-5-16 11:28
感谢回复。 但是 “GMATninja” 的解释说明了 选项A 是可以解释“he threshold of economic viability fo ...

他的意思就是: A选项cost决定的不是threshold,决定的是相对于threshold的位置, C才是能直接改变threshold的因素
发表于 2019-5-17 17:16:03 | 显示全部楼层
之前也困惑 现在搞清楚了 share一下

初始背景:虽然太阳能效率在上升,但 太阳能的单位成本 还是 比油要高的,也就是产生相同的电 太阳能还是比油要贵,之间有差距

题目在比较这个差距

本来按理解 太阳能效率升高应该使这个差距变小,但是却没变,问原因

能解释的一种原因就是 油的效率也上升了,所以没变

A选项 油价降了 单位油能产生的电应该比太阳能更多了 差距应该会更大

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