Having an efficient, attractive subway system makes good economic sense. So, the city needs to purchase new subway cars, since the city should always do what makes good economic sense.
The conclusion drawn above follows logically if which one of the following is assumed?
(A) The city should invest in an efficient, attractive subway system.
This simply restates the first clause of the last sentence in the passage. Out.
(B) Cost-effective subway cars are an integral part of an efficient subway system.
Cost-effective term makes this a bit extreme. Nothing about these cars being INTEGRAL is written either.
(C) Investment in new subway cars makes better economic sense than many of the other investment options open to the city.
Even if something else makes better economic sense - such as investing in maintaining roads - it does not mean that the city cannot ALSO invest in subway cars. Basically subway cars don't have to be the best option to be given an investment greenlight, since it ALSO makes economic sense.
(D) New subway cars are financially affordable.
Wow. This one was a very close second. The turning point comes when you consider that even IF the subway cars are not financially affordable (which I daresay you could simply read as being COSTLY) in the broader project aspect of the subway train system the passage states the the subway system makes ECONOMIC SENSE. So even if the cars are expensive, the overall end result makes economic sense anyway.
(E) New subway cars are required in order for the city to have a subway system that is efficient and attractive.
The answer. Try negating this and seeing what happens. Better yet note that the passage says that the subway cars are NEED-ed, but that this statement, when negated, would say they are NOT REQUIRED.
5 Verbal tips