The sumerians were among the first civilizations to develop a calendar based on the movement of the stars in the sky. why was a calendar important to the sumerians?
select one:
a. so they knew when the rivers were going to flood.
b. so they could tell when the trees were going to change colors.
c. so they knew when to expect traders from other civilizations.
d. so they knew when to make offerings to their gods.

The answer is,

a. So they knew when the rivers were going to flood,

because Mesopotamian civilization was built upon the "twin rivers" (the Euphrates and Tigris Rivers). When the rivers flood, the water would leave behind fertile soil (excellent for farming) when levels returned to normal, washing up minerals collected as the river followed its normal course of movement.

pretty sure they split up because of religious conflicts.

i think it was because of how protected egyptian civilization was was which allowed them to evolve without much outside influence.