user: Question: Opponent of Denver Broncos happened on what date?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Game site', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'text', 'real']
Sample row: [1.0, 'Sept. 12, 1976', 'Cleveland Browns', 'L 38–17', 'Cleveland Stadium', 67496.0]
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Opponent" = 'Denver Broncos';