user: Question: What is Opponent, when Date is December 18, 1988?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1.0, 'September 4, 1988', 'at Indianapolis Colts', 'W 17–14', 57251.0]
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Date" = 'December 18, 1988';