This map shows West Africa at the time of medieval empires. A map titled Medieval African Empires. 4 regions are shown with labels A through C. Region B includes the area from the west coast of North Africa, extends north slightly into the Sahara desert region, and moves east to Gao, encompassing the Senegal and Niger rivers. Region A does not extend to the coast, remaining within the area between the Senegal and Niger rivers, but extends north further into the Sahara region. Region C includes a small area on the west coast near a river, extends east past Gao, north into the Sahara desert region, and south of Djenne including most of the Niger River.
50 points plus whoever answers first
What does the B represent on the map?

the Mali Empire
the Songhai Empire
the trans-Saharan trade routes
the pilgrimage of Mansa Musa