user: Question: Who was the EP winning team when the CP winning team was Dave Clark and the GM winning team was Stuart Northrup?
Columns: ['Rnd', 'Circuit', 'AP Winning Team', 'BP Winning Team', 'CM Winning Team', 'CP Winning Team', 'DM Winning Team', 'DP Winning Team', 'EM Winning Team', 'EP Winning Team', 'FM Winning Team', 'FP Winning Team', 'GM Winning Team', 'GP Winning Team', 'HM Winning Team', 'HP Winning Team', 'Results']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1', 'Marlboro', 'Shelby', 'Chevrolet', 'Genie- Ford', 'Porsche', 'Ferrari', 'Triumph', 'Elva - Porsche', 'Porsche', 'Elva', 'Lotus', 'Lola', 'Triumph', 'Osca', 'Austin-Healey', 'Results']
SQL:

assistant: SELECT "EP Winning Team" FROM "Table" WHERE "CP Winning Team" = 'Dave Clark' AND "GM Winning Team" = 'Stuart Northrup';