United States Open(US Open) Tennis Championships 2019 is played on ______ surface ?

1) Grass
2) Clay
3) Carpet
4) Hard

Explanation:
US Open 2019 was the fourth and the last Grand Slam of 2019 hosted by the United States Tennis Association (USTA), other 3 being Australian Open, French Open & Wimbledon. ii. The total prize money of the tournament was $57,238,700 where singles champions received $3,850,000 & doubles champions received $740,000.