GWD 4 Q11

zy05833

Because ethlene dibromide, a chemical used to fumigate grain, was lamed for the hight rate of nerve damage suffered by people who work in grain-processing plants, many such plants swithed to other chimeical fumigants two years ago. Since then, however, the percentatge of wrkers at these plants who were nely diagnosed with nerve damage has not dropped significantly . therefore, either ethylene dibromide was wrongly blamed or else the new chemicals also caused nerve damage.
which of the following is an assumption on which the argument depends.
A: if the new chemicals caused nerve damage, the nerve damage caused would be different from any nerve damage that ethylene dibromide may caused.
B: there are no chemical fumgants that are completely safe for workers in grain-processing plants.
C: if ethylene dibromide causeds nerve damages, it does not take two years or longer for that damge to become detectable.
D: workers at grain-processing plants typically continue to wrk there even after eing diagonosed with nerve damage.
E: Workers at grain- processing plants that still use thylene dibromide continue to have a high rate of nerve damage.
求高人指导！

ViannaLIN

首先，不知LZ具体问题出在哪一选项，我认为A，B，D，E并不相关（这个可以用找premise, conclusion的方法多练感觉吧）；然后用了否定法确定C项正确。


否定法（因为assumption为必要条件，因此若必要条件被否定，则原结论必不成立）：
将C项变为 if ethylene dibromide causeds nerve damages, it DOES take two years or longer for that damge to become detectable.
If so, 这就是另一种可以解释 被诊断出nerve damage的工人percentage没有下降  的原因，并不是因为ethylene dibromide was wrongly blamed 或者 the new chemicals also caused nerve damage削弱了原结论，因此选C。


不知有木有帮助呀

ViannaLIN

另附上神帖！
http://forum.chasedream.com/GMAT_CR/thread-571267-1-1.html