做对了，但正确选项怎么看不懂？！

wynyy2000 · 发表于 2011-6-7 23:35:06

72. (30176-!-item-!-188;#058&005083)

A study followed a group of teenagers who had never smoked and tracked whether they took up smoking and how their mental health changed. After one year, the incidence of depression among those who had taken up smoking was four times as high as it was among those who had not. Since nicotine in cigarettes changes brain chemistry, perhaps thereby affecting mood, it is likely that smoking contributes to depression in teenagers.
Premise1: teenagers who are smokers are more likely evolved in depression than teenagers who are not
Premise2: nicotine changes brain chemistry that may affect mood
Conclusion: smoking causing depression in teenagers
Which of the following, if true, most strengthens the argument?
A. Participants who were depressed at the start of the study were no more likely to be smokers after one year than those who were not depressed.(如何理解？)
B. The study did not distinguish between participants who smoked only occasionally and those who were heavy smokers. Weaken
C. Few, if any, of the participants in the study were friends or relatives of other participants. Irrelevant
D. Some participants entered and emerged from a period of depression within the year of the study.
E. The researchers did not track use of alcohol by the teenagers. weaken

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.
科技发展，器械成本降低，但太阳能的经济成本没有降低
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. Irrelevant
B. The reduction in the cost of solar-power equipment has occurred despite increased raw material costs for that equipment. 那应该降低，没有解释
C. Technological changes have increased the efficiency of oil-fired power plants.
我怎么觉得C也没有解释为什么没有下降？理由：科技提高了燃油发电厂的效率，所以即使油价上涨，但output上升，控制了电价，跟太阳能发电一样经济，但是也没有解释为什么在太阳能,技术改进，机械成本降低下，价格不变？
D. Most electricity is generated by coal-fired or nuclear, rather than oil-fired, power plants. Irrelevant
E. When the price of oil increases, reserves of oil not previously worth exploiting become economically viable. Irrelevant

weixun1990 · 发表于 2011-6-8 11:30:10

第一题，题目没有排除的可能是：初始的时候实验对象depress的程度不一样，从而影响实验结果，即一开始比较depress的人后来容易吸烟，因而不一定是吸烟导致的depress，a选项排除了该种可能，即一开始比较depress的人与正常的人吸烟的可能性相同

hldada · 发表于 2011-6-8 18:11:59

第一题：
argument阐述：一年后那些染上抽烟习惯的人发生depression的可能性是不吸烟的四倍；也就是论述认为：吸烟导致depression
A: 那些一开始就depress的人与一般人相比，染上吸烟的可能性是一样的；
排除了 depression导致吸烟这一可能性；使吸烟导致depression的说法加强

hldada · 发表于 2011-6-8 18:21:11

第二题：
关键在于这个定义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)；
the threshold of economic viability for solar power ：想要让solar power plant 比 new oil-fired plant 更经济，而必须提高的每桶油的价格；
比方说生产相同的电量： oil-fired plant要花的钱（也就是油钱）+the threshold of economic viability for solar power （要上涨的相应的油钱）=solar power plant 要产生这些电量花的钱
文中又说技术发展使solar power plant 经济了，也就是说产生相同量的电他花的钱少了，但又说这个threshold of economic viability for solar power （要上涨的相应的油钱）一直也没变，唯一的可能就是oil-fired plant要花的钱也变少了，那只可能是因为C：oil-fired plant 也进步了，效率高了！
呵呵，更像数学题！

rasvoty · 发表于 2013-6-17 13:23:27

hldada 发表于 2011-6-8 18:21
第二题：关键在于这个定义the threshold of economic viability for solar power (that is, the price per ...

按照这个逻辑，不是A更像答案么？

sexybaby · 发表于 2013-10-8 15:52:42

假设之前石油的发电效率是m 度/桶,而每桶石油的价格是n 美金/桶,则单位发电成本为n/m.此时太阳能的每度电成本为T=(n+35)/m. 问题:若太阳能每度电成本T下降,而系数35不变,请问m,n该怎么变化?

答案有两个:N下降,或者M增加.或者N下降的同时,M增幅更大.所以这题的答案A或者C都可以.

kakadinho · 发表于 2013-10-19 21:01:31

这道题挺狡猾的，请注意黑体部分

Technological improvements and reduced equipment cost have made converting solar energy directly into electricity far more cost-efficient in the last decade. However, the threshold of economic viability is (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)unchanged at thirty-five dollars. 油价涨到多少钱一桶，就可以使得太阳能发电比传统烧油发电更经济，也就是成本更低，显然，太阳能一直成本更高，需要油价上涨来使得传统烧油的成本也上升，进而成本优势让给太阳能。“would have to rise” 说明threshold恰好等于使得两者成本相等的那个临界点的oil price。

设Cs是太阳能总成本，Cof（cost of oil-fired power plants)是oil-fired power plants(简称ofpp）的总成本，其中油成本为Coil，烧油发电的其他成本Cex。显然，Cof=Coil + Cex
而Threshold的定义，就是，使得这个等式成立的最小的Coil是多少：

Cs = Cof = Coil+Cex，注意这Coil是需要涨到的价格，和市场现在的价格无关。

现在，Cs由于Technological improvements and reduced equipment cost而下降，但是Coil却不变，等式还能成立，只能Cex下降。
也就是说，烧油发电中，除了油以外的那些成本下降了。只有C可以：整体效率提升 → 单位成本下降

A，在说oil的市场实际价格下降，但维持等式成立只需要的是“涨到的价格是35刀/桶”，和实际市场价格无关；（考虑A的都是把threshold当成增量了，觉得初始值下降了，增量不变，也可以解释等式右边的下降）
B 在加强premise，不能解释；
DE 明显的Irrelevant

做对了，但正确选项怎么看不懂？！

所属分类: GMAT考试

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