The best comparison from the options provided is:
Both monumental structures were built in capital cities as places to worship; the Aztec structure was a pyramid that signified two gods, whereas the Inca structure was rounded and signified one god.
This statement accurately reflects the monumental architecture of the Aztec capital (Tenochtitlan), which featured the Templo Mayor as a pyramid dedicated to multiple deities, and the Inca capital (Cusco), characterized by structures like the Coricancha, which was rounded and primarily dedicated to the sun god, Inti.