user: Question: Who sponsored Greg Biffle's win on April 14?
Columns: ['Season', 'Date', 'Winning Driver', 'Car #', 'Sponsor', 'Make', 'Distance', 'Avg Speed', 'Margin of Victory']
Types: ['real', 'text', 'text', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1997.0, 'April 6', 'Jeff Burton', 99.0, 'Exide Batteries', 'Ford Thunderbird', 'mi (km)', 'mph (km/h)', '4.067 sec']
SQL:

assistant: SELECT "Sponsor" FROM "Table" WHERE "Winning Driver" = 'Greg Biffle' AND "Date" = 'April 14';