Why were early civilizations usually located in large river valleys?

The people needed the water for drinking and growing plants, a skill learned during the Neolithic Revolution.

Explanation: River Valleys became ideal locations for cities and settlements because of the fertile land surrounding the river beds.

by using  production possibilities graph.  opportunity costs are key expenses in financial matters and are utilized as a part of registering money saving advantage investigation of a venture. such expenses, be that as it may, are not recorded in the record books but rather are perceived in basic leadership by processing the money costs and their subsequent benefit or misfortune.

a would be the answer