user: Question: What is the average Year when there was a Cosworth Straight-4 engine, and the Entrant was Ron Harris / Team Lotus?
Columns: ['Year', 'Entrant', 'Chassis', 'Engine', 'Points']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1963.0, 'Ecurie Maarsbergen', 'Porsche 718', 'Porsche Flat-4', 3.0]
SQL:

assistant: SELECT AVG("Year") FROM "Table" WHERE "Engine" = 'Cosworth Straight-4' AND "Entrant" = 'Ron Harris / Team Lotus';