The correct answer is - C. Songhai.
The Songhai Empire was one of the largest empires that the African continent witnessed on its soil. The empire stretched from the Atlantic coast, where Senegal and Gambia are now, occupying the northern portion of Western Africa, and large portion of the western Sahel, having the Niger River running in the middle of the empire.
The people living in this empire were Muslims, and they had accepted it before the empire was formed through earlier contacts with Muslims. As the empire grew stronger and larger, it incorporated lot of people that were not Muslims in it. The Songhai used their power and managed to convert most of the people on their territory to the Islam, thus spreading out the religion and strengthening it in the region.
