user: Question: Which opponent was on July 21, 2008?
Columns: ['Date', 'Tournament', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['July 21, 2008', 'ITF / Lexington, Kentucky', 'Hard', 'Carly Gullickson', '6–4, 6–2']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Date" = 'July 21, 2008';