The correct answer is D) Caliphates led to political and economic growth
While there had always been some level of trade, the boom of cities and empires made commercial activity in the African economy much more important. North Africa was central to the trade of the entire Mediterranean region. Outside of Egypt, this trade was mainly controlled by the Phoenicians who came to dominate North Africa, with Carthage as the most important city. The Greeks controlled much of the eastern trade, including that which occurred along the Red Sea with Ethiopia. In this region a series of Greek commercial cities were established and acted as a conduit for their civilization and learning.
During most of the first millennium AD, the Kingdom of Aksum in Ethiopia and Eritrea had a powerful navy and commercial links that reached the Byzantine Empire and India. Between the fourteenth and seventeenth centuries, the sultanate of Ajuran, centered in modern Somalia, practiced hydraulic engineering and developed new systems for agriculture and taxation, which continued to be used in parts of the Horn of Africa until the late nineteenth century.
