Who among the following has won the 2015 ATP World Tour Finals title ?
[A]Rafael Nadal
[B]S Wawrinka
[C]Novak Djokovic
[D]Roger Federer

Novak Djokovic
Novak Djokovic form Serbia won a record fourth straight ATP World Tour Finals with victory against Roger Federer. It is the fifth time in his career and earlier he had won it in 2008, 2012, 2013 and 2014. With this win, Djokovic surpassed previous record of Ivan Lendl’s set in 1987 after he had won his third straight Tour Finals title. With this victory, he ends the 2015 tennis season with 11 titles including three Grand Slams, taking his total to 10 titles.