CREATE TABLE table_58647 ("Season" FLOAT, "Date" CLOB, "Winning Driver" CLOB, "Car #" FLOAT, "Sponsor" CLOB, "Make" CLOB, "Distance" CLOB, "Avg Speed" CLOB, "Margin of Victory" CLOB)

Who sponsored Greg Biffle's win on April 14?
SELECT "Sponsor" FROM table_58647 WHERE "Winning Driver" = 'greg biffle' AND "Date" = 'april 14'
SELECT "Sponsor" FROM "table_58647" WHERE "Date" = 'april 14' AND "Winning Driver" = 'greg biffle'