title: Silverstone Circuit
context: Silverstone was first used for motorsport by an 'ad hoc' group of friends who set up an impromptu race in September 1947. One of their members, Maurice Geoghegan, lived in nearby Silverstone village and was aware that the airfield was deserted. He and eleven other drivers raced over a two-mile circuit, during the course of which Geoghegan himself ran over a sheep that had wandered onto the airfield. The sheep was killed and the car written off, and in the aftermath of this event the informal race became known as the Mutton Grand Prix.[8]
question: What was the first race held at the Silverstone Circuit?
answers: an impromptu race