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题库 / Prep2007E1-CR-17
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?
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.
At both schools, the plants in the greenhouses grew much more quickly than did plants planted outdoors in plots near the greenhouses.
The urban class conducting the experiment was larger than the rural class conducting the experiment.
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.
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.
我觉得a和e错误一样，都是在质疑前提，前提是二氧化硫含量高低影响植物生长速度，a选项在说城市挑选的学校二氧化硫含量不够高，抛开其他因素不看，这个实验可能无法得到城市农村明显的对比结果，e也是一样，勤换过滤网是想更有效的减少温室里二氧化硫的含量，同样会使得实验结果不明显。
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