CREATE TABLE table_52240 ("Res." TEXT, "Record" TEXT, "Opponent" TEXT, "Method" TEXT, "Event" TEXT, "Round" FLOAT, "Time" TEXT, "Location" TEXT)

Who was the opponent during the UFC 90 event with a fight that lasted less than 4 rounds?
SELECT "Opponent" FROM table_52240 WHERE "Round" < '4' AND "Event" = 'ufc 90'
SELECT "Opponent" FROM "table_52240" WHERE "Event" = 'ufc 90' AND "Round" < '4'