This is not specifically a strenghtening question. It is an exception. If true, each option would strengthen the argument (Except). So your thinking should switch to which option if it is in fact true does not strengthen the argument but weakens it? C. would weaken it because if Consumers already have a cynical attitude toward advertising it wouldn't impact the argument either way because it doesn't support why consumers should be skeptical or doesn't make an argument against. Unlike the other options, it serves no purpose and does not strengthen so it would be the exception.