user: Question: What type of surface was used for the game played on September 20, 1993?
Columns: ['Date', 'Tournament', 'Surface', 'Partnering', 'Opponents in the final', 'Score']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['March 2, 1992', 'Boca Raton , USA', 'Hard', 'Conchita Martínez', 'Larisa Neiland Natasha Zvereva', '6–2, 6–2']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Date" = 'September 20, 1993';