user: Question: What is the rider when the grid is 21?
Columns: ['Rider', 'Manufacturer', 'Laps', 'Time/Retired', 'Grid']
Types: ['text', 'text', 'real', 'text', 'real']
Sample row: ['Alex Barros', 'Honda', 30.0, '47:22.404', 2.0]
SQL:

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