Answer:
The correct answer is a. to serve as temples for the city's god or goddess.
Explanation:
Mesopotamian people believed that it was better to pray to the gods from a very close place because if the gods lived up in the sky you had to build great platforms to stay close to them.
The ziggurats were like sand-castles, so it was easy to get them to stay up.
An example of a ziggurat was the tower of Babel. In that story, people tried to build a ziggurat that could reach to Heaven. However, God didn't like that and he decided to destroy the ziggurat and dispersed people so they couldn’t try it again.
