What is the MAIN difference between Sunni and Shia Muslims?

Responses
A The Shia pray towards Mecca five times every day.The Shia pray towards Mecca five times every day.
B The Sunni believe in the idea of Monotheism.The Sunni believe in the idea of Monotheism.
C The Sunni fast from sunrise to sunset during the month of Ramadan.The Sunni fast from sunrise to sunset during the month of Ramadan.
D The Shia wanted a family member of Muhammad to succeed him.The Shia wanted a family member of Muhammad to succeed him.

D. The Shia wanted a family member of Muhammad to succeed him while the Sunni did not insist on Muhammad’s family member to succeed him as the leader of the Muslim community. This led to a split in the Muslim community in the early years of Islam.