user: Question: What was the surface of the match against Bethanie Mattek-Sands?
Columns: ['Outcome', 'Date', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', '5 February 2007', 'Carpet (i)', 'Gabriela Navrátilová', 'Cara Black Liezel Huber']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Opponent" = 'Bethanie Mattek-Sands';