Final answer:
The Sumerians believed in a theocratic system of government, as evidenced by the significance of the temple and the belief that the entire city belonged to its main god.
Step-by-step explanation:
The excerpt provides evidence for option C, that the Sumerians believed in a theocratic system of government.
According to the passage, the temple was the largest, tallest, and most important building in the city, indicating its significance in the Sumerian society. The belief that the entire city belonged to its main god and had been assigned to the god since the creation of the world suggests a theocratic system of government, where the god was recognized as the ruler and state officials operated on the god's behalf.
Additionally, the passage mentions that the priestly governors ruled over these temples, reinforcing the idea of a theocratic system of government in which religious authority played a central role.