user: Question: Which opponent was playing on December 20, 1998?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'TV Time']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'September 7, 1998', 'at Denver Broncos', 'L 27–21', 'ABC 9:00pm']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Date" = 'December 20, 1998';