Who works harder, Justin Bieber, the Kardashians or Robert Pattinson?

The Kardashians sisters said they are the stars of the moment, andwhich are filled with work. So the gossip website Hollywoodlifeasked: Do you really think they work more than Justin Bieber?
According to the website, the Kardashians said they work long hours, and get very upset when they say they are famous for nothing.
Justin Bieber, 17, lives busy doing shows, giving interviews. In recent weeks Justin has visited six cities, including Paris, Oberhausen, and Nottingham.