The correct answer to this question would be alternative D) "It contributed to the rise of power city-states and later kingdoms."
Africa is a very large continent with many nations and a lot of area of wilderness, or that hasn't got the best weather and soil conditions for farming.
Since regions are really decentralized, trade contributed to the rise of Power City-States such as Mombasa, Gede, Lamu, and Malindi, and that contributed to the formation of African Kingdoms