Concept:The Almoravids (al-Murabitun) were led by Abdullah b. Yasin, who introduced their movement to West Africa.Explanation:Yahya b. Ibrahim invited Abdullah b. Yasin to lead and spread the Islamic reform movement.Abdullah b. Yasin then became the spiritual leader of the Almoravids.It was Abdullah b. Yasin who brought the al-Murabitun movement into West Africa.The other leaders listed were not the one who introduced it.Answer:B. Abdullah b. Yasin