Answer: All these economies rested on agriculture thanks to the fertile plains around the river valleys
Explanation: Ancient Mesopotamia grew up in the valley of the Tigris and Euphrates rivers, India along the Indus River and Egypt in the Nile Valley. This means that on the basis of rich agricultural yields, they could gradually develop, enrich over the time and use the same rivers to transport goods and exchange goods, which was a precondition for progressing to the size of civilizations as we know them from history.
