扫描二维码，直接登录
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.
果因？
错选B。 greenhouse外面的植物状况如何不能够影响任何城市和郊区的比较，属于无关选项。
实验中排除了二氧化硫的影响，如果两地植物生长一样，则说明了实际二氧化硫影响大；如果城市植物仍生长慢，肯定是有除二氧化硫以外其他因素导致生长慢.D项列出了其他影响实验因素。
登录 或 注册 后可以参加讨论