作者：英吉
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.
问题分析：
A说学校主要坐落在sd这种物质相对较低的地方，说学校在什么地方，文章反复再谈论的是sd的含量和植物增长速度之间的关系，这个选项内容和原文没有什么关系，杀。
B 说温室的植物和外面的植物那个长的快，这两种植物的对比原文没说过，杀。
C 是说两个地方做的试验那个地方更大，没说过，杀。
D 说城市的某用因素（这种因素可以是交通也可以是其他东西，不重要，我可以随意编）能够影响植物（光只是个media），文章反复在谈的就是城市和乡村sd含量对植物的影响，留着。
E 说变化频率那个快，显然无关，杀。
