CREATE TABLE table_27991 ("Series #" FLOAT, "Episode title" CLOB, "Directed by" CLOB, "Written by" CLOB, "Original air date" CLOB, "Prod. code" FLOAT)

Who wrote the episode with production code 5?
SELECT "Written by" FROM table_27991 WHERE "Prod. code" = '5'
SELECT "Written by" FROM "table_27991" WHERE "Prod. code" = '5'