I believe the answer is b because there were often wars between African clans and the best way to get rid of the prisoners and get things they needed at the same time was to trade them.
Answer: mesopotamia
Explanation: Sumer, located in Mesopotamia, is the first known complex civilization, developing the first city-states in the 4th millennium BCE. It was in these cities that the earliest known form of writing, cuneiform script, appeared around 3000 BCE.
The answer is A. Hope it helps