The Olmec were the earliest people to settle in Mesoamerica. They were an advanced people who established trade connections with neighboring empires such as the Maya v. They thrived from 1500 BC to 800 BC. However, the reasons for their decline are
unclear

There isn't a certain reason but scientist speculate it was environmental change and the people were cut off from food supply.

(d) rivers.

explanation:

civilizations developed around rivers because their waters provided places to hunt and fish. also, as the rivers flooded, the lands around them became fertile. this allowed them to support farming. this is especially true of the nile river, which flooded the same time each year.

the answer is option a.