user: Question: Name the average points for chassis of stevens and year less than 1950
Columns: ['Year', 'Entrant', 'Chassis', 'Engine', 'Points']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1950.0, 'Murrell Belanger', 'Stevens', 'Offenhauser L4', 0.0]
SQL:

assistant: SELECT AVG("Points") FROM "Table" WHERE "Chassis" = 'stevens' AND "Year" < 1950.0;