求助，费解的一道题

supercury

17.   

Urban air contains more sulfur dioxide than does rural air, and plants in cities typically grow more slowly than do plants in rural areas.  In an experiment to see how much of the difference in growth is due to sulfur dioxide, classes in an urban and a rural school grew plants in greenhouses at their schools and filtered the greenhouse air to eliminate sulfur dioxide.  Plants in the urban greenhouse grew more slowly than those in the rural greenhouse.

Which of the following, if true, would it be most important to take into account in evaluating the result?

(A) The urban school was located in a part of the city in which levels of sulfur dioxide in the air were usually far lower than is typical for urban areas.
(B) At both schools, the plants in the greenhouses grew much more quickly than did plants planted outdoors in plots near the greenhouses.
(C) The urban class conducting the experiment was larger than the rural class conducting the experiment.
(D) Heavy vehicular traffic such as is found in cities constantly deposits grime on greenhouse windows, reducing the amount of light that reaches the plants inside.
(E) Because of the higher levels of sulfur dioxide in the air at the urban school, the air filters for the urban school's greenhouse were changed more frequently than were those at the rural school.
答案是D 请问为什么不是E呢？帮忙分析分析吧！！！！

eeheaven

Reading comprehension. The passage ask you to EXPLAIN the fact that "Plants in the urban greenhouse grew more slowly than those in the rural greenhouse." If the filter at both green house filters out most of the sulfur, then how could the growth rates are still different at the two schools? So, B) alone cannot explain this fact in the passage, unless you have eveidence that the sulfur level is higher in one greenhouse than in another.

flyfairy019

But B) reveals the difference in growth rate between plants growing in sulfur (outside greenhouse) and those in non-sulfur environment (in the greenhouse), so B) at least proves that sulfur does influence the plant growth, even though there're still other reasons for the difference between city and urban.  Could you explain it more? Thanks!

eeheaven

then what about B? we can compare the plants in the greenhouse with the outdoors, then get the resut ...
citidandan 发表于 2011-10-21 20:19

  Unfortunately, B) does not give you any hints about the effect of sulfur on plant growth, which is the goal of the current study. The only conclusion you can get from B) is that plants growing in greenhouse grow faster than those growing outside the greenhouse. What's the cause? We do not know.

citidandan

then what about B? we can compare the plants in the greenhouse with the outdoors, then get the resutls. since i think the purpose of the experiment is to to see how much of the difference in growth is due to sulfur dioxide, not the difference in urban and rural.

eeheaven

What the stimulus gives you is a paradox. The hypothesis to explain the difference in growth rate of urban plants vs. rural plants is that the different concentration of SO2 causes this difference in plant growth. But when growing the plants at rural location with SO2 removed from the air, the difference still remains. What happened? Is the hypothesis wrong?

Well, D) says the hypothesis might still be good since something else in the city (blocking more sunshine) might caused the unexpected experimental result.

E) on the other hand won't help explaining the unexpected result mentioned above. It only proves that the SO2 in urban air is more than that in rural air. We know that already from the stimulus.

charles1992

D中 that favors predominantly male occupations over those that are predominantly female

后面那个those that are 很累赘。就像 I gave him more money than that was given to you.

gmat改错中正确答案很少这么啰嗦的，遇到这样的句子尽量找简洁的。

a514116402c

我是这样想的 如果按照E的说话城市的过滤器更换更频繁，那么对二氧化碳吸收能力更好，所以说植物应该长得快嘛，和事实相反了，所以不是那个问题