Who has become the oldest player in the world to hold number 1 rank in the ATP world rankings?

Who has become the oldest player in the world to hold number 1 rank in

1.	Who has become the oldest player in the world to hold number 1 rank in the ATP world rankings?
A.	Ruben Bemelmans
B.	Grigor Dimitrov
C.	Roger Federer
D.	Philipp Kohlschreiber
Answer» D. Philipp Kohlschreiber