Why Was Islam So Readily Adopted by Rulers Within the Sudan

Why was Islam so readily adopted by rulers within the Sudan?

A) They were all conquered by overwhelming Muslim armies and forcibly converted to Islam.
B) The Muslim concept of a ruler who united civil and religious authority reinforced traditional ideas of kingship.
C) The Muslim concept of religious equality allowed rulers to dispose of the traditional clans and lineages of Africa.
D) As a monotheistic religion, Islam was much like the traditional religions of Africa.