The transition from hunter-gatherer to a food producing society happened a. to the unstable nature of pastoralism. b. gradually in the Mesolithic era c. abruptly in some areas, rapidly in others d. with the use of metal tools. e. only in river valleys

e. Only in river valleys.

Explanation:

Why? Agriculture needs the proximity of water and the development of methods of irrigation in order to prosper. Agricultural societies were the basis of the first civilizations. In the Middle East, in China, in Egypt, all the first great civilizations rose and flowered in valleys with rivers: the Eufrates and the Tigris, the Yellow River and the Yangtze, and the Nile.