user: Question: What Rider has a Grid of 21?
Columns: ['Rider', 'Manufacturer', 'Laps', 'Time', 'Grid']
Types: ['text', 'text', 'real', 'text', 'real']
Sample row: ['Álvaro Bautista', 'Aprilia', 20.0, '42:56.428', 2.0]
SQL:

assistant: SELECT "Rider" FROM "Table" WHERE "Grid" = 21.0;