请教OG-153

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.

这道题的提干那位给解释一下呀？尤其是括号里的成分，是什么意思？在整个的逻辑结构中有什么作用？谢谢了！！

第一句：太阳能发电成本下降

第二句：但其经济上可行的门槛还是：35刀。

eonomic viabilty是指：当油价是多少时，使用太阳能才能和使用燃油成本相同。

这题的中心就是：虽然太阳能自身成本降低了，但由于油价也在降，而且降的更快，所以太阳能在和燃油的竞争中还是不具备价格优势。

呵呵，上面的妹妹解释得似乎对，但答案选错了！

呵呵，抱歉，确实是我错了，（我做题时就错了，还一直没发现～）

前面三句说的是对的，后面重新解释：

油价和economic viability（threshold）的比较是人们选择oil还是solar时需要进行的比较，这里题目想问的是threshold本身为什么没下降，所以油价的升降是后话了。

因为：在solar技术提高时，oil的技术也提高了，economic viability这个反映相对关系的量就没有下降。

要是还有错误，请继续指正！

文中说明:Threshold=the price per barrel, 这个价钱在new solar power plants to be more economical than new oil-fired power plants的情况下会have to rise,但是现在是unchanged at thirty-five dollars,所以必然的结论是new solar power plants not to be more economical than new oil-fired power plants, 则推出 Technological changes have increased the efficiency of oil-fired power plants.

火力cost－太阳能cost＝Threshold=the price per barrel=35,

当太阳能cost下降时,Threshold(the price per barrel)应该supposed to rise, 但是unchanged,所以火力cost必然下降.

I read a lot of explaination here, but I still can not convince myself that A is incorrect.

"the price per barrel to which ..." is talking about the price... I think it matches "the cost of oil" perfectly.

Help!!! Any NN?

If gains in cost-efficiency of solar power have not improved its economical viability relative to oil-derived power, the explanation must be that oil-derived power itself has become more cost-efficient. Choice C points to this explanation and is thus the best answer.

Actual oil prices control how far, given the viability threshold, solar power is from economic viability but do not figure in the determination of the threshold, so choices A and E are incorrect. Choice B provides background on data that give rise to the puzzle but leaves the puzzle unresolved, so it is incorrect. Because the viability threshold for solar power is defined in relation to generating electricity from oil, choice D is irrelevant to determining the threshold and thus incorrect.

请大家再仔细看一下OG的解释。OG解释说，油价本身的升降，以threshold为标准衡量的话，只和太阳能离economic viability有多远有关，而不影响threshold本身。也就是说，这个threshould指得是太阳能与燃油两种能源的efficiency之间的区别，而不是指价格的区别。

我对这题的解释，很罗嗦，对否，请指教。

比如：发1千瓦时的电，用太阳能的成本是35美元；发同样多的点，需用油一桶。如果一桶油的价格高于35美元，当然，大家都会选择太阳能，因为这是经济的。因此经济适用性的起限实际上是太阳能的成本。现在，技术水平提高了，用太阳能，35美元可以发10千瓦时的电。如果一桶油仍然只能发一千瓦时的电，那么经济适用性的起限自然会降低。只有一桶油的利用效率提高到可以发10千瓦时的电，那么经济适用性的起限，自然会回到35美元。因此，OG说，真实的油价，只能决定太阳能真正成为经济能源，还有多长的路要走，而不能决定经济适用性起限的本身。

这题有意思，做错了，看了有关帖子，受很大启发，总结一下。

First：   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也就是说，为了使新的太阳能发电厂比新的以石油为燃料的发电厂更经济，石油必须涨到的每桶价格。

Second：  threshold通俗的说就是一个临界值或界限，本题说的是solar power 相对于oil-fired 发电的经济可行的临界值。

Third：太阳能发电厂单位发电成本用cost of sun表示

        新的以石油为燃料的发电厂单位发电成本用cost of oil plant表示

   则   cost of oil plant＝单位发电耗油量x油价＋other costs

   如果使新的太阳能发电厂比新的以石油为燃料的发电厂更经济，则应有

        cost of sun≤cost of oil plant， 即

        cost of sun≤单位发电耗油量x油价＋other costs

   当cost of sun＝单位发电耗油量x油价＋other costs时，油价临界值出现，油价＝35。

  如果如题所述cost of sun减少，而油价不变时，则单位发电耗油量或other costs必须减少，换句话说就是cost of oil plant减少，也就是oil plant效率提高，选项C正确。