Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_44688 ( "Tournament" text, "Surface" text, "Week" text, "Winner and score" text, "Finalist" text, "Semifinalists" text )

### Question ###
On what surface did they play the match in the week of October 21?

### Accurate SQL ###

SELECT "Surface" FROM table_44688 WHERE "Week" = 'october 21'