The correct answer is C) The Maya and Aztecs developed calendars of 365 days.
The statement about astronomy in Mesoamerica that is TRUE is "The Maya and Aztecs developed calendars of 365 days."
Let's have in mind that Mayans were expert astronomers who observed the starts to make predictions. One of those calendars was called the Haab. It was a solar calendar of 365 days that was divided into 18 months with 20 days. It included 5 extra days. Another important calendar was the Tzolkin. It was the divine calendar with 260 days, divided into 20 periods of 13 days. To track longer periods, they used the Long Count Calendar.
The original Aztec calendar craved in stone can be visited in the spectacular Museum of Anthropology located in México City.