user: Question: What is the surface for the Volos tournament?
Columns: ['Date', 'Tournament', 'Surface', 'Opponent in final', 'Score', 'Prize Money']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['May 21, 2006', 'Antalya', 'Hard', 'Çağla Büyükakçay', '6-3 6-2', '$10,000']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Tournament" = 'Volos';