user: Question: What team was the opponent on 1990-10-21?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Venue', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, '1990-09-09', 'San Diego Chargers', 'W 17–14', 'Texas Stadium', '48,063']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Date" = '1990-10-21';