He information above relates to the historical development of West Africa. "One of the main aspects of the development of West African kingdoms was the emergence of cities. The first city, Koumbi Saleh, grew on the edge of the Sahara where the Kingdom of Ghana developed around it. Further inland, three bustling centers emerged along the Niger river: Djenne, Timbuktu, and Gao. These cities were the major sites of trading activity in the Malian Empire. Gao eventually broke from a declining Mali and created the Songhai Empire."

Which conclusion is supported by the information and your knowledge of West Africa?

A Outside influences caused cities to decline.
B Exhaustion of resources forced cities to change
C Trading centers promoted regional development.
D Conflicts among cities hindered cultural advancement.