user: Question: WHAT WAS THE SURFACE MADE OF WHEN THE OPPONENT WAS George Khrikadze?
Columns: ['Edition', 'Round', 'Date', 'Against', 'Surface', 'Opponent', 'W/L', 'Result']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['2007 Davis Cup Europe/Africa Group I', '1R', '9–11 February 2007', 'Georgia', 'Carpet', 'George Khrikadze', 'Win', '6–3, 7–6 (7–5)']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Opponent" = 'George Khrikadze';