请教逻辑OG-153

gu946

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.
答案是C,我选的是A,我的分析:扩号中已经明确对threshold进行
了说明,threshold由必须增加的price决定.如果solar energy变的
far more cost-efficient,那么如果oil方面没有变化的话,threshold
变小了(也就是oil需要增加的价格减少了),这样,oil价格减少的话
就可以保持threshold不变了.我这样分析有没有问题?C也有道理,
不过关系不够直接,还要由efficiency of oil-fired power plants,推
价格的关系,我觉得还不如A好.但答案是C,为什么?OG的解释是:
(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.)
我不太明白.

[此贴子已经被作者于2003-8-1 21:44:56编辑过]

cranberry

不多说，提醒一点，即文中比较的是用石油的火力发电站和太阳能发电站发电的成本，而油价只是成本的一部分，C说效率更高了，即单位成本的产出更多，平均成本下降

lifelover

cranberry的解释如一盏明灯啊...xiexie.

xiebinustc

这题这样理解比较好：

当油价为35时，太阳能电和火力电价格持平，即：

太阳能cost=35+火力cost，太阳能cost－火力cost＝35，当太阳能cost下降时，

等式继续成立，所以火力cost必然下降，这里与油价没有关系。

ercizhang

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.

ercizhang

第4楼的公式应为:火力cost－太阳能cost＝35,

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

yvonne09122001

也就是說油價只是利用火力發電成本的一部份,所以就算油價大跌,火力發電的總成本也不一定下跌(可能還牽涉其他的成本 如人事成本等)  是這樣詮釋的嗎?

如果是的話 為何題目要針對threshold的定義 限定是 "the price per barrel to which oil would have to rise" (特別提出油價呢?  為何不說是 the cost of oil-fired plants wold have to rise to make the solar power more economical)  因為油價的變換的確是會影響threshold 但不但表示絕對性的影響,所以我覺得很奇怪,為何定義要針對油價

謝謝

ya-ya

既然石油价格只是石油发电厂成本中的一部分，那么４楼和６楼的公式都不对把，题目中关于threshold的定义是： 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，既然是"rise", 那一定和石油的现价密切相关，试用公式表示如下：

石油发电成本＝n*石油价格＋a     (假设是线形函数，n,a为参数）

则threshold需满足：太阳能发电成本＝石油发电成本＝n*（石油现价＋threshold)+a

这样一来，C选项就不对了，因为石油发电成本降低并不能确定threshold的变化（石油现价不确定）；而Ａ选项则是正确的：虽然太阳能发电成本降低，但石油现价也降低，则可能导致threshold不变。

请ＮＮ帮忙看看我是哪里分析错了呢

[此贴子已经被作者于2005-1-24 6:11:48编辑过]

ya-ya

顶....

ya-ya

期待NN进来讨论啊......