The option which was not one of the purposes of mythology is the third option - myhology was an ancient ritual initiating a boy into manhood. These rituals are rites of passage, and have nothing to do with mythology which is made of made-up stories about something. These stories were usually created in order to explain something happening in nature, as well as to entertain people when there was nothing else to do. Mythologies are also a valuable resource of knowledge about past cultures and their societies.
