What Was One of the Major Differences Between African Civilizations

What was one of the major differences between African civilizations and other post classical societies?

A) African civilizations built somewhat less clearly on prior societies than did other post classical societies.
B) African civilization was almost entirely dependent on cultural importations from Islam and the Arabic world.
C) Prior to 800, African civilizations had no prior contacts with civilizations outside of the African continent.
D) There were no civilizations in Africa until the post classical period.