CREATE TABLE table_28110 ("Series #" FLOAT, "Season #" FLOAT, "Title" TEXT, "Director" TEXT, "Writer ( s ) " TEXT, "Airdate" TEXT)

Who directed the episodes that aired December 15, 1956?
SELECT "Director" FROM table_28110 WHERE "Airdate" = 'December 15, 1956'
SELECT "Director" FROM "table_28110" WHERE "Airdate" = 'December 15, 1956'