user: Question: what is the surface when the opponent is Selma Babic?
Columns: ['Edition', 'Round', 'Date', 'Against', 'Surface', 'Opponent', 'Result']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['2002 Fed Cup Europe/Africa Group I', 'RR', '24 April 2002', 'Bulgaria', 'Clay', 'Desislava Topalova', '6–7 (4–7) , 1–6']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Opponent" = 'Selma Babic';