CREATE TABLE "table1_21726793_1" (
  "no" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" text,
  "u_s_viewers_million" text
);

Question: who directed the production code 2t5710?
SQL: SELECT "directed_by" FROM "table1_21726793_1" WHERE "production_code"='2T5710';

Question: what is the total number o production code where us viewers is 2.76?
SQL: SELECT COUNT("production_code") FROM "table1_21726793_1" WHERE "u_s_viewers_million"='2.76';

Question: who wrote the no 2?
SQL: SELECT "written_by" FROM "table1_21726793_1" WHERE "no"=2;