What date was the Silverstone circuit driven? 
{'header': ['Race Name', 'Circuit', 'Date', 'Winning driver', 'Constructor', 'Report'], 'page_title': '1950 Formula One season', 'section_title': 'Non-Championship race results', 'caption': 'Non-Championship race results', 'rows': [['XI Pau Grand Prix', 'Pau', '10 April', 'Juan Manuel Fangio', 'Maserati', 'Report'], ['II Richmond Trophy', 'Goodwood', '10 April', 'Reg Parnell', 'Maserati', 'Report'], ['V San Remo Grand Prix', 'Sanremo', '16 April', 'Juan Manuel Fangio', 'Alfa Romeo', 'Report'], ['IV Grand Prix de Paris', 'Montlhéry', '30 April', 'Georges Grignard', 'Talbot-Lago', 'Report'], ['XII British Empire Trophy', 'Douglas', '15 June', 'Bob Gerard', 'ERA', 'Report'], ['IV Gran Premio di Bari', 'Bari', '9 July', 'Giuseppe Farina', 'Alfa Romeo', 'Report'], ['IV J.C.C. Jersey Road Race', 'Jersey', '13 July', 'Peter Whitehead', 'Ferrari', 'Report'], ["XII Circuit de l'Albigeois", 'Albi', '16 July', 'Louis Rosier', 'Talbot-Lago', 'Report'], ['I Grote Prijs van Nederland', 'Zandvoort', '23 July', 'Louis Rosier', 'Talbot-Lago', 'Report'], ['III Grand Prix des Nations', 'Geneve', '30 July', 'Juan Manuel Fangio', 'Alfa Romeo', 'Report'], ['I Nottingham Trophy', 'Gamston', '7 August', 'David Hampshire', 'Maserati', 'Report'], ['IV Ulster Trophy', 'Dundrod', '12 August', 'Peter Whitehead', 'Ferrari', 'Report'], ['XIX Coppa Acerbo', 'Pescara', '15 August', 'Juan Manuel Fangio', 'Alfa Romeo', 'Report'], ['I Sheffield Telegraph Trophy', 'Gamston', '19 August', 'Cuth Harrison', 'ERA', 'Report'], ['II BRDC International Trophy', 'Silverstone', '26 August', 'Giuseppe Farina', 'Alfa Romeo', 'Report'], ['III Goodwood Trophy', 'Goodwood', '30 September', 'Reg Parnell', 'BRM', 'Report']]}