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.