user: Question: how many times is the chassis brabham bt33?
Columns: ['Year', 'Entrant', 'Chassis', 'Engine', 'Points']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1955.0, 'Cooper Car Company', 'Cooper T40', 'Bristol Straight-6', '0']
SQL:

assistant: SELECT COUNT("Year") FROM "Table" WHERE "Chassis" = 'brabham bt33';