请教一道老题 GWD-2-19

grape262001

Sunflowers growing in pots were placed, with their roots submerged, in the pond contaminated with radioactive elements.  The sunflowers kept growing; in the process, they absorbed radioactive elements.  Within twelve days, 85 percent of the radioactive elements were removed from the water, which is no less than can be accomplished with the much more expensive conventional filtration techniques.  Scientists therefore propose using sunflowers for decontamination wherever there are radioactively contaminated ponds.

Which of the following, if true, points to a limitation on the applicability of the proposed method of decontamination?    D

A.      Some plants other than sunflowers can also remove radioactive elements from water.

B.       The water in many ponds contaminated with radioactive elements is so cold that it would kill sunflowers whose roots were submerged in it.

C.      Sunflowers that grow with their roots submerged in water grow less well than sunflowers growing under optimal conditions on dry land.

D.      Only species of sunflowers with large leaves can have their roots submerged in water and still keep growing.

E.       In ponds in which the circulation of the water is artificially increased, sunflowers absorb radioactive elements far faster than they do in other ponds.

答案给出的是B，我当时选的时候是D。我看了一下以前的帖子，不是很详细。题目问的是LIMITATION，我觉得B和D都有这种限制。但我个人感觉还是D贴近一些。

请不吝赐教！

yi11

问题说的limitation说的是对结论有limitation而不是说对推理的条件有limitation。而文章的结论是推荐使用向日葵对在有辐射的水塘减少辐射。
(D)说的是只有大叶子向日葵才能根在水下继续生长，即使(D)对，使用向日葵可以减少辐射还是成立的，不冲突。注意结论是向日葵的可使用性(applicability)，而不是向日葵本身。另外(D)应该很好排除，因为文章没有指定那种向日葵，而(D)限定了向日葵的范围，scope change可以排除。

grape262001

谢谢，顺便再问一个问题。我觉得我做题的时候很多时候都错在这个范围的问题上？是否说题目中没有给出范围的，选项也不能选限定范围的？

但是我记得以前有看过一些题目答案就是以题目中所述的现象是一种特例来WEAKEN的。

请赐教

yi11

我觉得不能一概而论，重点还是要看结论和结论的范围
另外具体问题的用词也很重要，GMAT/LSAT很多题都是在限定词上做文章
比如这题文章要是all sunflowers can be used to decontaminate，(B)就是weaken。

[此贴子已经被作者于2008-8-7 11:43:26编辑过]

grape262001

谢谢！