user: Question: Who did he play on a Hard surface?
Columns: ['Outcome', 'Date', 'Tournament', 'Surface', 'Partner', 'Opponents', 'Score']
Types: ['text', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Winner', 1991.0, 'Florence , Italy', 'Clay', 'Ola Jonsson', 'Juan Carlos Báguena Carlos Costa', '3–6, 6–1, 6–1']
SQL:

assistant: SELECT "Opponents" FROM "Table" WHERE "Surface" = 'Hard';