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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. 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.
这道题我没太懂，不是说要看how much of the difference in growth is due to sulfur dioxide么？ 那做实验应该一个用sulfur dioxide一个不用作对比么. 为什么这里两个一个农村一个城市都用 filtered the greenhouse air to eliminate sulfur dioxide
都filter了还比什么呀？？？？
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发表于 2013-10-2 01:02:34
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