Argument 1: Governments are justified in trying to prevent cigarette ads, because they promote unhealthy behavior.
Argument 2: Cigarette ads should remain legal as long as fatty food ads are legal, because both encourage unhealthy practices.
These two statements conflict, unless there is a distinction between prevention and complete illegality. That is the key to answering this question. Which answer choice offers such a distinction, so that the author's two statements can coexist?
I was able to eliminate A, B, and C pretty quickly, but I had to think about D and E for a minute.
The problem with E is the last phrase, "but should not try to prevent such advertisements." The author's first argument says that the government can justifiably prevent cigarette ads. E conflicts with this statement, so it is incorrect.
D gives us what we need. Financial disincentives are a way to prevent cigarette ads, but this is not the same as outlawing them entirely. This is one way to reconcile the author's arguments, so it is the correct answer.