Table: broncos_1981_season
Columns: week
date
opponent
result
game_site
record
attendance

Question: What is the opponent played on October 4?
SQL: SELECT "opponent" FROM broncos_1981_season WHERE "date" = 'October 4'

Question: Where is riverfront stadium the game site for the week?
SQL: SELECT MIN("week") FROM broncos_1981_season WHERE "game_site" = 'Riverfront Stadium'