CREATE TABLE table_57068 ("Grand Prix" TEXT, "Date" TEXT, "Location" TEXT, "Pole Position" TEXT, "Fastest Lap" TEXT, "Winning Driver" TEXT, "Constructor" TEXT, "Report" TEXT)

Who had the fastest lap of the race that Ayrton Senna won on 23 April?
SELECT "Fastest Lap" FROM table_57068 WHERE "Winning Driver" = 'ayrton senna' AND "Date" = '23 april'
SELECT "Fastest Lap" FROM "table_57068" WHERE "Date" = '23 april' AND "Winning Driver" = 'ayrton senna'