On what type of surface was the tournament of Italy f28?
CREATE TABLE "doubles_titles_21" (
  "date" text,
  "tournament" text,
  "surface" text,
  "partner" text,
  "opponent_in_the_final" text,
  "score_in_the_final" text
);
SELECT "surface" FROM "doubles_titles_21" WHERE "tournament"='italy f28';