user: Question: Which Surface has an Opponent of Oleksandra Kravets?
Columns: ['Outcome', 'Date', 'Tournament', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', '28 January 2003', 'Tipton', 'Hard (i)', 'Matea Mezak', '6–4, 4–6, 4–6']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Opponent" = 'Oleksandra Kravets';