Final answer:
Ziggurats in Sumerian cities were primarily used by priests as religious and political symbols of power, not accessible to the general public but reserved for important rituals conducted to venerate the city's patron deity.
Step-by-step explanation:
The ziggurats in Sumerian cities served primarily as religious and ceremonial sites. These massive structures were not ordinary places of worship accessible to the general public. Instead, they were reserved for priests and authorized religious officials to perform rituals and tend to offerings for the gods. Ziggurats like the Nanna Ziggurat at Ur and the Anu Ziggurat in Uruk were impressive architectural achievements that symbolized the connection between the divine and the theocratic governance of the city. Their design as stepped pyramids with a temple or shrine at the top allowed them to stand out as centers of power, both religious and political.
In reference to the provided options, the correct usage for ziggurats was by priests as symbols of their religious and political power. Therefore, the correct answer is b) Priest as symbols of power.