Final answer:
The division between Sunni and Shia Islam is based on whether a caliph must be a descendant of the Prophet Muhammad, with the Shia affirming and Sunni denying this requirement.
Step-by-step explanation:
The question that separated the two branches of Islam, Sunni and Shia, is D) Must a caliph be descended from Muhammad? The Shia believe that the leadership should reside within the Prophet Muhammad's family, through his son-in-law Ali, while the Sunni do not require that a caliph be a descendant of Muhammad. This division arose immediately following the death of Muhammad, as the Muslim community had to consider who should succeed him. The Shia branch of Islam believes that the leadership should reside in the family of Muhammad only through his son-in-law Ali, while the Sunni branch, which is larger, does not specifically require leadership to come from Muhammad's descendants through Ali.