GMATPrep CR question

[bakshi.puneet]

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?

A. More of the cars in Donia's capital city were made before 1993 than after 1993
B. The number of new cars sold per year in Donia has declined slightly since 1993.
C. Pollutants other than nitrogen dioxide that are emitted by automobiles have also been significantly reduced in Donia since 1993.
D. Many Donians who own cars made before 1993 have had catalytic converters installed in their cars
E. Most car trips in Donia's capital city are too short for the catalytic converter to reach its effective working temperature.

I was stuck between A and E. Chose E, which happens to be the correct answer.

Can somebody (if possible Ron/Stacey) help me differentiating between A and E?
Is my reasoning below to through out A correct ? If so, is the same reasoning not true with E as well ?

A.
One of the premise says,
"proportion of new cars in Donia’s capital city has always been comparitively high". which means,
(%age new cars) in capital > (%age new cars) in other cities
Option A says that in capital, number of old cars is greater than no of new cars, which could very well be true. But, it is still possible that people in Donia's capital use old cars with additionally installed catalytic converter. We don’t know. Hence OUT.

E.
With almost similar reasoning as above, is "effective working temperature" not out of scope here? This may or may not be the contributing factor.

[boaz.khan]

It cannot be A since they clearly tell you that "the proportion of new cars in Donia's capital city has always been comparatively high". I looked at A for a couple seconds but then re-read the premise - E is the correct answer.