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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.
本题中，对于我来说，最难排除的是A，如果新车比旧车数量少的话，那么安装该种设备之后，似乎减少的不会太多，请各位大N帮忙解释一下，多谢！
如果文中把下面的这句话去掉，是否A也对？ －and as a result, nitrogen dioxide emissions have been significantly reduced throughout most of the country； | 
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发表于 2004-10-10 22:14:00
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