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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.
为什么A不对呢
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选D

这道题讲的是greenhouse的试验,外面的空气质量和题目无关。是干扰选项。
应该选D。因为阳光也是造成greenhouse植物生长缓慢的原因。
希望可以帮到你

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我也觉得D是对的
但是我觉得sulfur dioxide是影响试验结果的啊 如果这个URBAN地区不能代表整个URBAN 那试验

结果就不能说明问题啊

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