user: Question: On what surface did they play the match in the week of October 21?
Columns: ['Tournament', 'Surface', 'Week', 'Winner and score', 'Finalist', 'Semifinalists']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Indian Wells', 'Hard', 'March 11', 'Michael Chang 7–5, 6–1, 6–1', 'Paul Haarhuis', 'Goran Ivanišević Marcelo Ríos']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Week" = 'October 21';