The conclusion of the argument is "There is evidence, however, that some advertisers are motivated by moral as well as financial considerations." What is this evidence? After a family oriented publication switched its focus to sex and violence, some advertisers withdrew their advertisements from it. This is a cause and effect argument. The observed effect the author is trying to explain is the advertisers withdrawing their ads after this change and the author's proposed cause for this observed effect is moral disapproval of salacious material now being published.
To strengthen this argument, we need to try and show that the reason behind withdrawing their ads was in fact morally based, as opposed to financially based.
(A) is incorrect because though it seems to strengthen the idea that the advertisers did move back towards their original audience of family newspapers, we do not know whether the motivation behind this was based on morals or finances. Perhaps having their ads in family newspapers is more profitable for the advertisers, and therefore, their motivations, though seeming to be morally-driven, are still actually financially driven. This is a trap answer choice.
(B) is incorrect because it seems to weaken the argument, in that there is more evidence towards the belief that the advertisers are not morally motivated since they are moving towards a more salacious publication.
(C) is CORRECT because it clearly points out how leaving the publication is not going to be good for the advertisers financially, but yet they still left. Therefore, answer choice (C) completely eliminates the possible alternative cause that the advertisers's decision could have been financially motivated. So it strengthens the conclusion that they were, in fact, morally motivated.
(D) is incorrect because the fact that there is little overlap between those who read family magazines and those who are likely to buy newspapers that concentrate on sex and violence is irrelevant to whether or not the advertisers move was morally or financially motivated.
(E) is incorrect because we do not know what income group the changed publication is going to appeal to. It might appeal to a better income group which could be evidence of financial motives for the advertisers.
Hope that was helpful! Let me know if you have any other questions.
