What was the nationality of the swimmer in the semifinal with a time of 29.51?
CREATE TABLE "women" (
  "event" text,
  "date" text,
  "round" text,
  "name" text,
  "nationality" text,
  "time" text,
  "record" text
);
SELECT "nationality" FROM "women" WHERE "round"='semifinal' AND "time"='29.51';