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.
答案：D
之前做错了。最近重做，还是错了。
哪位高人能指点一下？选D是为了排除他因？
另外，题目中的这个实验：农村和城市的学校都将plant放在温室里，而且filtered the greenhouse air to eliminate sulfur dioxide，这样的话，如何看出sulfur dioxide 的区别？
many thx！！！作者: dreamistrue 时间: 2011-10-22 01:12
这是个对照实验 说明sulfur dioxide已经不是造成这个现象的原因 所以只能是它因,也就是D-different amount of light" 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.不选E，选D。 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.作者: sbdk 时间: 2011-11-26 23:59
个人对于B、D选项的理解 重点在实验的目的： an experiment to see how much of the difference in growth is due to sulfur dioxide
lants in the urban greenhouse grew more slowly than those in the rural greenhouse.