As of October 2020, the highest number of French Open tennis tournaments have been won by:

Correct option is D

The Correct Answer is: (d) Rafael Nadal

Explanation:
As of October 2020, Rafael Nadal holds the record for the most French Open titles in the history of tennis. He won his 13th French Open title on 11 October 2020, defeating Novak Djokovic in the final. This victory further cemented his reputation as the "King of Clay", given his unparalleled dominance on the red clay courts of Roland Garros, Paris.

Information Booster:
• Nadal’s 13 French Open titles (2005–2020) account for more than half of his total Grand Slam wins.
• He remained undefeated in French Open finals up to 2020.
• The 2020 final marked Nadal’s 100th match win at Roland Garros.
• Nadal equaled Roger Federer's record of 20 Grand Slam titles with this win in 2020.
• The French Open is one of the four Grand Slam tournaments, held annually in May–June, but the 2020 edition was delayed to September–October due to COVID-19.
• Nadal’s physical endurance and powerful top-spin forehand have made him the most successful clay court player in history.