The correct option is A The need to concentrate population away from arable lands near rivers.
Mesopotamian civilizations formed on the banks of the Tigris and Euphrates rivers in what is today Iraq and Kuwait. Geologic factors were of primary influence on where and how the ancient Mesopotamian civilization (3500–1500 B.C.) developed. River sedimentation and weathering resulted in a fertile soil on an alluvial plain, thus insuring the surplus food supply that was the basis for an urban culture and civilization. The need to concentrate population away from arable lands near rivers, was not a deciding factor in the development of Mesopotamian civilization.