GWD24-29我怎么觉得没有正确答案哩？

GWD-24-29.          GWD_TN_10_29

Plant scientists have been able to genetically engineer vegetable seeds
        to produce crops that are highly resistant to insect damage. Although
        these seeds currently cost more than conventional seeds, their cost is likely to decline. Moreover, farmers planting them can use far less pesticide, and most consumers prefer vegetables grown with less pesticide,
        therefore, for crops for which these seeds can be developed, their use is likely to become the norm.

Which of the following would be most useful to know in evaluating the
        argument above?

A.      Whether plant scientists have developed insect-resistant seeds
        for every crop that is currently grown commercially

B.       Whether farmers typically use agricultural pesticides in larger
        amounts than is necessary to prevent crop damage.

C.      Whether plants grown from the new genetically engineered seeds
        can be kept completely free of insect damage.

D.      Whether seeds genetically engineered to produce insect-resistant
        crops generate significantly lower per acre crop yields than do
        currently used seeds.

E.       Whether most varieties of crops currently grown commercially have
        greater natural resistance to insect damage than did similar varieties in the past.

答案是D

看过以往的讨论 大家争论的焦点在于BDE

E是过去情况和现在情况的对比，题干未涉及，是无关项

B叙述的内容与题干相悖，即使算不上相悖也是无关项

D我认为也是无关项，亩产量的问题在题干中并未涉及

请指正

我觉得选ｃ，觉得就ｃ还有点与原文讨论的东西有关联－insect damage，其他的选项好象风马牛不相及。

望ＮＮ指教！！！

谢谢你的解答

不过我觉得你对D的解释不严谨 有主观臆断的成分

为什么亩产量下降一定会使cost上升？

请大哥指教

另外，我倾向于选B

但是在权威答案面前不知到底作何选择

大家都来讨论一下吧

个人认为，commercial的问题MM应该考虑到几个问题：1收入、2成本、3利润（3=1-2）

premise:cost is likely to decline(because:farmers planting them can use far less pesticide);revenue is likely to increase(because:most consumers prefer vegetables grown with less pesticide);so margin profit is likely to increase(3=1up-2down)

conclusion:their use is likely to become the norm

D选项，亩产和收入强烈相关，因为收入=产量*价格，亩产增加，收入有增加的趋势；相反，则有减少的趋势。利润亦如此，从而评估了become the norm的可能性。

B farmers planting them can use far less pesticide，所以farmers typically use agricultural pesticides这个问题是没有什么作用的，不管conventional seeds用多少pesticides, genetically engineer vegetable seeds 都会用的比它要少，成本是必然降低的。

希望有帮助。

谢谢详细的解答

不过我还是要问了 呵呵

即使亩产量降低，但是这种新品种的价格很可能会因为人们的喜欢而上升啊

如果是这样的话即便亩产量降低农民的收入不一定会降低啊

也许是我钻牛角尖了

不好意思了

恩恩，所以我没说一定会让收入增加，只是有增加的趋势，作者也没有说价格的趋势会怎么样，在已知信息的情况下，当然是产量高support,产量低weaken,题目没有要求证明充分性，所以price是怎样的趋势是不需要知道的。

明白了

谢谢

这个充分性必要性的原理怎么运用啊？

看到好多CDer都提到了，我不太明白。

mm,这个话题一两句说不清。

参见

http://forum.chasedream.com/dispbbs.asp?BoardID=24&ID=61430