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题库 / Prep2008E2-CR-104
Nitrogen dioxide is a pollutant emitted by automobiles. Catalytic converters, devices designed to reduce nitrogen dioxide emissions, have been required in all new cars in Donia since 1993, and as a result, nitrogen dioxide emissions have been significantly reduced throughout most of the country. Yet although the proportion of new cars in Donia's capital city has always been comparatively high, nitrogen dioxide emissions there have showed only an insignificant decline since 1993.
Which of the following, if true, most helps to explain the insignificant decline in nitrogen dioxide emissions in Donia's capital city?
More of the cars in Donia's capital city were made before 1993 than after 1993.
The number of new cars sold per year in Donia has declined slightly since 1993.
Pollutants other than nitrogen dioxide that are emitted by automobiles have also been significantly reduced in Donia since 1993.
Many Donians who own cars made before 1993 have had catalytic converters installed in their cars.
Most car trips in Donia's capital city are too short for the catalytic converter to reach its effective working temperature.
情景： 本题讲述了在Donia减少二氧化氮排放的故事。推理文段用了Donia的大部分地区作为案例，推理到Donia首都地区的情况。
答案预估：
直接解释为何“Donia的首都二氧化氮的排放量没怎么减少”即可。
选项分析：
A选项：更多Donia首都的车是1993年以前生产出来的。即便是有更多的车是1993年之前生产的，原则上只要有一部分的新车，就应该能减少排放。
B选项：Donia每年卖出的新车的数量自从1993年开始下降。本选项错误和A相似。
C选项：除了二氧化氮外的机动车排放的污染物自从1993年也开始下降了。本选项和要解释的现象无关。
D选项：许多拥有1993年以前生产的车的Donia人已经在自己的车里装了一个催化剂转换器了。本选项和要解释的现象无关。
E选项：Correct. 大部分Donia的首都的车程太短了如此以至于催化剂转换器无法达到其有效工作温度。若催化剂转换器无法达到有效的工作温度，那么在首都，转换器装在新车上与不装在新车上是完全没有区别的，自然不能减排。
不过为什么D不对？如果1993年前大家都已经装了转换器，那么变化值确实不会很高？
题目给出的信息是 proportion of new cars 高，但是污染没有减少很多，要解决的是新车内部的矛盾，而不是旧车的情况。
况且如果旧车都有装置了，新车比例又大，那污染肯定应该下降很多，选项也无法解释这个矛盾。
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