Why were river systems important in supporting early civilizations and in them flourish?

a. they provided transportation to import food.
b. they were the only source of food for early civilizations.
c. they provided water for irrigation and agriculture.
d. they were natural barriers which prevent attacks.

I believe its C.

Explanation:

Water wasn't there only source of food because they were hunters and gatherers. They caught game( squirrels, rabbits, and other animals). Because this is early civilization they were figuring out how to use crops for food. So C should be the answer.

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