user: Question: what team played on April 21
Columns: ['Date', 'Opponent', 'Score', 'Loss', 'Save']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['April 1', 'at Minnesota Twins', '7-5', 'Miceli', 'Aguilera']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Date" = 'April 21';