The correct answer is C) they enable campaigns to sample the public opinion.
The statement that best describes how social-networking sites help political campaigns, especially when compared to traditional media is that they enable campaigns to sample public opinion.
One of the great advantages of social media sites over traditional media when referring to advertising a political campaign is the possibility of sampling public opinion. Since the first political campaign of Barak Obama in 2008, his campaign team used digital political marketing strategies to reach new audiences. This created a huge advantage over his adversary that basically limited his campaign on traditional media. So using digital marketing on social-networking sites, the advisors and campaign teams are able to simple public opion due to the interaction users have when visiting these sites.