prep 逻辑的一道题求解释

dpan92

有牛人能解释一下这道逻辑题怎么做吗？？？？

Urban air contains more sulfur dioxide than does ruralair, and plants in cities typically grow more slowly than do plants in ruralareas.  In an experiment to see how muchof the difference in growth is due to sulfur dioxide, classes in an urban and arural school grew plants in greenhouses at their schools and filtered thegreenhouse air to eliminate sulfur dioxide. Plants in the urban greenhouse grew more slowly than those in the ruralgreenhouse.

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

(A) The urban school was located in a part of the city inwhich levels of sulfur dioxide in the air were usually far lower than istypical for urban areas.

(B) At both schools, the plants in the greenhouses grewmuch more quickly than did plants planted outdoors in plots near thegreenhouses.

(C) The urban class conducting the experiment was largerthan the rural class conducting the experiment.

(D) Heavy vehicular traffic such as is found in citiesconstantly deposits grime on greenhouse windows, reducing the amount of lightthat reaches the plants inside.

(E) Because of the higher levels of sulfur dioxide in theair at the urban school, the air filters for the urban school's greenhouse werechanged more frequently than were those at the rural school.

南瓜小小

答案是B吗？求答案

dpan92

我也觉得可能是b，但非常不确定

yongsf

应该选D
原文说Urban air contains more sulfur dioxide than does rural air导致了urban　grow　slowly。为了验证sulfur dioxide对于生长速度的影响程度就做了一个对比实验，在urban和rural的green　house里种树，都排除了sulfur dioxide的干扰（green　house的空气中不含sulfur dioxide），结果urban　仍旧grow　slowly。
问如何评价。
D说的是城市中的尾气啊还是什么的使得greenhouse的窗户很脏遮挡住了阳光。这样破坏了对照试验。本来城市和乡村的各种客观条件是一样的而且都没有sulfur dioxide，城市的仍然慢，就可以说明不是sulfur dioxide的原因。但是D提出其他条件是不一样的，就不能证明了。
B说grennhouse内外的比较。题目里说的是rulal和urban的比较，所以是不相干的。

dpan92

太感谢了！！！