CREATE TABLE table_27534 ("Round" TEXT, "Circuit" TEXT, "Date" TEXT, "Pole Position" TEXT, "Fastest Lap" TEXT, "Winning driver" TEXT, "Winning team" TEXT)

Name the winning driver for 20 april
SELECT "Winning driver" FROM table_27534 WHERE "Date" = '20 April'
SELECT "Winning driver" FROM "table_27534" WHERE "Date" = '20 April'