Once there was a food surplus, complexity within early river civilizations increased, as did according to the archaeological record.

Once there was a food surplus, complexity within early river civilizations increased, as did , according to the archaeological record.

Explanation:

Mesopotamia, land between rivers, its economy, as in many other fluvial civilizations, was based mainly on agriculture. The first Neolithic settlements settled in fertile areas, generated surplus agricultural and livestock that allowed them a progressive increase in population, crafts, and trade.

This transformation required the control of the course of the rivers to guarantee the crops.

The answer is: The population.

ok sorry the answer is a. by their religion

letter a is the answer