The country of Maravia has severe air pollution, 80 percent of which

Exactly my thought process. However, I slightly differed when I came across the words transportation system for many years in option C. This means the factor of transportation is NOT changing, its a constant.

Also in the passage it says 80 percent of which is caused by the exhaust fumes of cars. Notice fumes of CAR causes pollution. Public transportation consists mainly of trains and buses. You can only consider cars as public transport when they are for e.g. "share taxis".

I had a similar experience - both D and E weaken to some extent. It is just a decision of which option weakens more:

Option D says that disposable income is enough so increasing prices will not affect the sales of cars.
Option E says that the cars that emit low levels of pollution are anyway cheap. However if people are anyway not buying cheap cars, how will increasing the taxes on some cars make sure that people go for cheap cars?

Do you notice that E is actually not a weakener its a strengthener, If the car proposed in the question

cars that emit relatively low levels of pollutants cost 10 percent less to operate, people will start buying these cars. And if it so happens the pollution should be less than its present value. So the govt, plan works.

I think I can help you with this question, government's plan is to increase tax in order to reduce numbers of cars on the road, hence reducing overall pollution.
E is a completely different plan by adopting a low emission car. You have to stick to the original argument.
Hope it helps.

E is completely irrelevant. You don't know how was the situation before Tax . You have no information after tax implementation.

OG ans is A but the correct answer is D. If anyone can prove me wrong, let me know.
(A) The government of Maravia is in the process of building a significant number of roadways.
(D) Ninety percent of the population of Maravia is very prosperous and has a substantial amount of disposable income.

OG ans explains for A states new road does not necessarily equates more car usage, they can render unused, while D they suggest people are wealthy hence new tax will have less effect on people.

Both A and D require assumption / inference, however A contains a better assumption than D. It is because: a government's decision to build new roadways would always be based on some level of consultation / demand-supply analysis, as a result it is unlikely to build empty road and waste tax payer's money, time, resource and efforts; note also the phrase "building significant number of roads" - let's say at least some car will be added to the road.

On the other hand one, ans D require assumption of human psychology that if you are wealthy you are less sensitive to tax. This assumption is based plainly on stereotype and can be arbitrary, and I know very well, from my personal experience / studies, that wealthy people are wealthy because they are smart / sensitive about money. elasticity and people's reaction to tax pretty much depends case by case. Hence, unlike ans A that has an assumption that is based on common government practice / logical rationale, ans D is more susceptive to challenge. A is a better argument.

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