Many of the early civilizations began along major river systems. The main reasons listed in the passage inlude:
A.
The river systems provided these early civilizations with a consistent source of silt from the yearly floods for crops.
B.
The river systems provided these early civilizations with water for the crops.
C.
The silt from the yearly floods is like a natural fertilizer, bringing new minerals to enrich the crop depleted soil.
D.
The river systems provided these early civilizations with an easy transportation.