While mesopotamia met its primary challenge by decentralizing, egypt's response was to unify and remain so during most of its history. what was this challenge?

efforts to support large scale agriculture

(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.