user: Question: What is Surface, when Opponent is "Jiří Vaněk"?
Columns: ['Date', 'Tournament', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['19 July 2004', 'Tampere , Finland', 'Clay', 'Boris Pašanski', '6–2, 3–6, 6–2']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Opponent" = 'Jiří Vaněk';