What key discovery laid the foundation for wealthy, urban native societies in places like mexico?

Agricultural surpluses, this encouraged population growth as more food and preserving methods were discovered which enabled societies to extend the life of food through storage. With the ability to grow more food as well as have innovative methods for keeping it, the gateways for trade, urban growth, and market places for commodities grew and laid the foundation for wealthy, urban natives societies.

Ithink the answer you are looking for is (b).