What compelled celebrities to become more active in the 2012 political campaigns according to politico. com's article celebs get political in 2012?

The article in Politico suggests a couple of possible reasons for the celebrity involvement in the 2012 election like for one Barack Obama's star power and liberal appeal plus because of the social media boom which makes the communication much, much easier. Finally this kind of communication with the stars also works well. 

The answer should be b.