There are two major sects of Islam, or groups with different beliefs: the Sunnis and the Shias, or Shiites. The split between Sunni and Shia Muslims goes back to 661, when the fourth caliph after Muhammad, a man named Ali, was killed. A big disagreement ensued about who should be the next caliph. Sunnis believed that the first four caliphs, or heirs to Muhammad, were his rightful successors. Their descendants ruled the Arab world until after World War I. The Shias were (and still are) a smaller group. They thought that only one of those first four caliphs was legitimate—the one named Ali—and only his heirs should rule. It might seem like a small difference, but it meant that these people were telling their rulers, "You don't have the right to rule us." There is still a lot of tension between these two sects today. Which of these is the key difference between Sunnis and the Shias?

A
Sunnis believe that the first four caliphs were Muhammad’s rightful successors, while the Shias believe that only Ali was legitimate and only his heirs should rule.

B
Sunnis believe that a caliph should be the leader of the Muslim religion, while Shias believe that a caliph should only lead the government.

C
Sunnis believe that only Ali and his heirs should rule, while Shias believe that the first four caliphs were Muhammad’s rightful successors.

D
Sunnis believed that the first four caliphs were Muhammad’s rightful successors, while the Shias believed that the first three caliphs were Muhammad’s rightful successors.