user: Question: What suface during the game that had Yevgeny Kafelnikov as an opponent?
Columns: ['Outcome', 'Date', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', '13 October 1997', 'Hard (i)', 'Fabrice Santoro', '4–6, 4–6']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Opponent" = 'Yevgeny Kafelnikov';