The most accurate answer would be B. as the empire expanded, those with political and religious power became leaders and ruled with other city-states.
The ancient Mayan civilization operated as a series of independent city-states, but as political and military alliances formed, leaders who held religious and political power were able to establish influence over multiple city-states, leading to a degree of centralization. This process was often facilitated by marriages, warfare, and the establishment of trade relationships among the various city-states.