The correct answer is D) nomadic tribes.
Paleolithic humans consisted of hunters and gatherers who divided themselves into small nomadic tribes.
These people were nomads because they were hunters that followed the herds to hunt animals to feed their families. Everything changed during the Neolithic Revolution when ancient humans learned agriculture techniques and settled in some territories to grow crops. One example could be ancient Sumeria. People settled in the middle of the Euphrates and Tigris Rivers, in the Middle East region of modern-day Iraq.