Who was the opponent during the UFC 90 event with a fight that lasted less than 4 rounds?
CREATE TABLE "mixed_martial_arts_record" (
  "res" text,
  "record" text,
  "opponent" text,
  "method" text,
  "event" text,
  "round" real,
  "time" text,
  "location" text
);
SELECT "opponent" FROM "mixed_martial_arts_record" WHERE "round"<4 AND "event"='ufc 90';