user: Question: What circuit did Juan Manuel Fangio have the fastest lap at the German Grand Prix?
Columns: ['Race', 'Circuit', 'Date', 'Pole position', 'Fastest lap', 'Winning driver', 'Constructor', 'Report']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Argentine Grand Prix', 'Buenos Aires', '13 January', 'Stirling Moss', 'Stirling Moss', 'Juan Manuel Fangio', 'Maserati', 'Report']
SQL:

assistant: SELECT "Circuit" FROM "Table" WHERE "Fastest lap" = 'Juan Manuel Fangio' AND "Race" = 'German Grand Prix';