when was the premiere of the episode where the amount of North American spectators was 1.76 millions?
CREATE TABLE "table1_21979779_1" (
  "no" real,
  "num" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);
SELECT "original_air_date" FROM "table1_21979779_1" WHERE "u_s_viewers_million"='1.76';