Answer:
D. Africans always let their slaves go free after two years of service.
Step-by-step explanation:
It is true that slavery existed in Africa long before European contact. This was an important institution for African people, and is is one that allowed the trasnsatlantic slave trade to develop. However, slavery in Africa was significantly different from slavery in America. Slaves were usually more intergrated into their communities, and were not forced to work as hard as they did in the New World.