Who was the away team when Manchester United played at home on 10 February 1951?
CREATE TABLE "fifth_round_proper" (
  "tie_no" text,
  "home_team" text,
  "score" text,
  "away_team" text,
  "date" text
);
SELECT "away_team" FROM "fifth_round_proper" WHERE "date"='10 february 1951' AND "home_team"='manchester united';