freemanfanmao
GMATNinja
The explanation you quoted is spot-on. The passage very clearly indicates that there's a big difference between (1) what happened in the capital and (2) what happened in most of the country. Why is it that NO2 emissions barely declined in the capital while NO2 emissions were significantly reduced throughout most of the country?
(D) fails to explain that difference. All else being equal, we would expect (D) to have the same impact on emissions everywhere in the country (including the capital). After all, if (D) is true, then ANY car (new or old) can have a catalytic converter and thus can have lower NO2 emissions. That means that the new tech should lower NO2 emissions everywhere, regardless of the proportion of pre-1993 vehicles... so why the discrepancy in the data?
(E) is the only one that explains the difference, so it's the only choice that works.
I hope that helps!
Thanks Charles for the reply and confirmation. So if (D) said "Many Donians
in the capital who own cars made before 1993 have had catalytic converters installed in their cars.", then it would be a possible correct answer to the question right?
Thanks.
In general, it's not worth changing answer choices and assessing the versions that you've developed. Your task is to evaluate the answer choices on the page, so it's not a great use of your time to come up with your own versions.
Even with the change that you've made, (D) doesn't explain why NO2 emissions haven't gone down that much. We'd also need to know
when these capital-dwellers installed the catalytic converters to make a meaningful assessment. If they were installed
before 1993, then your adapted answer choice might explain why NO2 emissions haven't changed much. If they were installed
after 1993, we'd actually expect NO2 emissions to be reduced even
more than emissions outside of the capital.
As you can see, messing around with answer choices can lead to further complications. Luckily, to be really good at GMAT CR, you don't need to go down that rabbit hole.
I hope that helps!