Answer:
b. conflict over who should be the caliph
Explanation:
Prophet Muhammad died without a male heir neither did he choose a successor. This led to a conflict between two major groups. one group wanted that someone from the family of Muhammad should be chosen for the position of caliph while others who were in majority, Sunna ( an elite Muslim community ) to decide it in favor of Abu Bakr. Thus the followers of Ali and later his son Hussein are called Shias while the other are known as Sunnis.
