As at 04 December 2017 who was No 1 in the tennis world rankings?

Question

Tennis player Monica Seles turned pro in 1989 and was the year-end world no. 1 in 1991 and 1992. How old was she when she turned pro?

Answer 1

Rafael Nadal
Nadal returned in 2017 from struggles with injury and a loss of form to climb back to his No 1 ranking with his win in the 2017 US Open. The win marked the first time that Nadal had captured two Grand Slam tournaments in a year since 2013. Federer was No 2 at 25 September.