user: Question: Who's the opposition at Westpac Stadium when the attendance is 31,853?
Columns: ['Date', 'Round', 'Attendance', 'Opposition', 'Stadium']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['26 August 2007', 'Round 1', '14,421', 'Melbourne Victory', 'Westpac Stadium']
SQL:

assistant: SELECT "Opposition" FROM "Table" WHERE "Stadium" = 'Westpac Stadium' AND "Attendance" = '31,853';