How many rankings did the 5th season have?
CREATE TABLE "american_television_ratings" (
  "season" text,
  "timeslot" text,
  "season_premiere" text,
  "season_finale" text,
  "episodes" real,
  "tv_season" text,
  "ranking" text,
  "viewers_in_millions" text
);
SELECT COUNT("ranking") FROM "american_television_ratings" WHERE "season"='5th';