The rise of the first river-valley civilizations (Mesopotamia, Egypt, Indus Valley, and Yellow River basin between roughly 3500 and 1600 BCE) was MOST directly enabled by which combination of factors?
AReliable water from rivers, fertile alluvial soils that supported intensive agriculture, and a resulting agricultural surplus that supported non-farming specialists (rulers, priests, artisans).
BCold, arid conditions that eliminated the need for water management.
CIsolation from all trade routes and neighboring populations.
DUniform political systems imposed by a single external empire.
Explanation
River-valley civilizations rose where reliable water and fertile alluvial soils supported intensive agriculture. The resulting agricultural surplus enabled specialization — rulers, priests, artisans, soldiers — that in turn supported urban development, writing, and monumental architecture. Options B–D contradict documented archaeological evidence.