All of the following are true statement about slavery in africa except?

This is a tough question, If I'd have to guess I say the answer is D. Africans let their slaves go free after two years of service.
Slavery has existed on the earth almost since the beginning and has been present on every continent and still exists today. so I doubt it's B.   A. and C. I'm not sure about but I'm pretty sure that D. is false.
Good luck.