The youngest Greek tennis player, who won the ATP Finals 2019 title by beating Dominic Thiem is ______ ?

1) Matteo Berrettini
2) Roger Federer
3) Jo-Wilfried Tsonga
4) Stefanos Tsitsipas

Explanation:
On November 17, 2019, Greek professional tennis player, Stefanos Tsitsipas (21) has won the ATP (Association of Tennis Professionals ) World Tour Finals trophy (officially 2019 Nitto ATP Finals) by beating world No.5 Dominic Thiem of Austria with 6-7 (6-8) 6-2 7-6 (7-4) scores in O2 Arena ,London (United Kingdom) on November 17, 2019. He also earned a prize money of $2,656,000.