请教OG-153

babydevil

ETS这题出的肯定有毛病，注意看题目怎么问的：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?
注意问的是why not decrease threshold，threshold就是太阳能离economic viability的差距，题目问的就是差距为什么没减小，而不是threshold为何依然存在。
OG答案否定A的说法是：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
油价可以控制how far离economic viability的差距,但不能决定threshold，这不是抽自己嘴巴吗？

wingkim

以下是引用lfeng08908在2005-6-22 0:26:00的发言：

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。

同意这样的理解，题目的问题主要还是对“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) ”的理解。跟上面的解释相似，threshold应该理解成“为了使solar power plants比new oil－fired plants 更加节约时油价应该达到的最大对应值（非真实油价），也就是说并非由油价来决定threshold和是否economical，而是在太阳能发电成本必须比燃油发电成本经济的情况下决定的对应油价”。题目已经限定了对应油价不变，所以A选项根本就不对；而且太阳能成本下降了，那么就只能从燃油效率方面优化。

[此贴子已经被作者于2005-7-16 0:32:05编辑过]

gonghao

up

huangyh03

以下是引用携隐在2005-5-25 16:56:00的发言：

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。

看了一遍，所有的讨论就les和携隐斑竹的说到了解题的关键