有谁能给说说这个题E选项为什么不对吗？！！

cloudylee

17.    (27669-!-item-!-188;#058&003302)

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.  lants 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.

E中air filter也会影响growth的啊，为什么不加入考虑？

wyw1018

你的意思是说filter换得频繁会使植物生长慢？

四月小朋友

这道题讲的是一个测试除了sulfur dioxide会不会有其他因素影响植物生长的实验。
两个地方的实验做法就是用过滤器把两者的空气都过滤掉，然后看还有什么因素可以影响。
这要求在sulfur dioxide方面，两个地方的实验条件必须一模一样。
如果是E选项的话，城市地区的市过滤器换的比较勤，就没办法判断最后的结果到底是因为sulfur dioxide过滤得更完全导致还是有别的原因。
不是大牛，说错莫怪~