user: Question: Who was the Class D winner in round 6?
Columns: ['Round', 'Circuit', 'Date', 'Class A Winner', 'Class B Winner', 'Class C Winner', 'Class D Winner']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1', 'Snetterton Motor Racing Circuit , Norfolk', '14 April', 'John Love', 'Alan Hutcheson', 'None (no entries?)', 'Mike Parkes']
SQL:

assistant: SELECT "Class D Winner" FROM "Table" WHERE "Round" = '6';