user: Question: What couple averaged 21.0?
Columns: ['Rank by average', 'Competition finish', 'Couple', 'Total', 'Number of dances', 'Average']
Types: ['real', 'real', 'text', 'real', 'real', 'text']
Sample row: [1.0, 1.0, 'Jill & Darren', 371.0, 11.0, '33.7']
SQL:

assistant: SELECT "Couple" FROM "Table" WHERE "Average" = '21.0';