What type of surface was used for the game played on September 20, 1993?
CREATE TABLE table_6977 (
    "Date" text,
    "Tournament" text,
    "Surface" text,
    "Partnering" text,
    "Opponents in the final" text,
    "Score" text
)
SELECT "Surface" FROM table_6977 WHERE "Date" = 'september 20, 1993'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: What type of surface was used for the game played on September 20, 1993? ### Input: CREATE TABLE table_6977 (
    "Date" text,
    "Tournament" text,
    "Surface" text,
    "Partnering" text,
    "Opponents in the final" text,
    "Score" text
) ### Response: SELECT "Surface" FROM table_6977 WHERE "Date" = 'september 20, 1993'