Who were the 3rd couple that were viewed by 4.89 million viewers? 
CREATE TABLE "series_2" (
  "num" real,
  "airdate" text,
  "no_of_couples" real,
  "1st_couple" text,
  "2nd_couple" text,
  "3rd_couple" text,
  "4th_couple" text,
  "viewers_millions" text,
  "itv1_weekly_ranking" text
);
SELECT "3rd_couple" FROM "series_2" WHERE "viewers_millions"='4.89';