D) is the correct answer.
The original difference between the Sunnis and the Shias was they disagreed on who should have succeeded Muhammad .
About 15% of Muslims belong to Shiism. They are in favor of which the caliphs (responsible of the government) must be descendants of the prophet Muhammad and that the correct successory line is the one drawn up by Ali, cousin and son-in-law of the Prophet Muhammad.
On the other hand the Sunnies are the main branch of Islam and, although they coincide in the majority of the religious aspects with the Shiites, they do not agree with the premise on the line of succession of the Caliphs. Generally the countries belonging to Sunism have governments elected according to criteria specific to each particular population.