The correct answer is: B: Myth.
Myths or Origin Myths are the stories we tell to explain how things came to be, and every culture has them. These myths try to describe the origin of some feature of the natural or social world. They are merely accounts given to try to explain what has happened before our time.
The other options refer to different stories:
Folktales are meant to give an explanation to things people did not understand, to discipline children or to simply pass the time. Fiction refers to any narrative that is derived from the imagination and Legends are non-historical or unverifiable stories handed down by tradition from generation to generation and popularly accepted as historical.