The answer is A: have lives and stories of their own
A side character or supporting character is a character in any form of narrative that is not the focus of the main plot or storyline, but, rather, appears often in the narrative, developing a story line of his or her own, which can be quite complex, although it is not completely independent of the main story line. Usually the side character´s story is presented in order to make the narrative´s main story line more complete.
