Who was the opponent of the match in South Dakota, United States which has 2 rounds?
CREATE TABLE "mixed_martial_arts_record" (
  "res" text,
  "record" text,
  "opponent" text,
  "method" text,
  "event" text,
  "round" real,
  "location" text
);
SELECT "opponent" FROM "mixed_martial_arts_record" WHERE "round"=2 AND "location"='south dakota, united states';