Final answer:
The letter identifying the location of the Aztec civilization on the map is A. MEXICO, where the historic city of Tenochtitlan was located, corresponding to present-day Mexico City.
Step-by-step explanation:
The letter identifies the location of the Aztec civilization on the given map as A. MEXICO. The Aztec Empire was located in central and southern Mexico, and its most famous city, Tenochtitlan, was built on an island in Lake Texcoco, which is now the site of modern-day Mexico City. Based on the historical texts, Mesoamerica, the region where the Aztecs developed their civilization, extended from north of Panama up to central Mexico, but it was in the Valley of Mexico where the Aztecs built their impressive city. Over time, this civilization expanded its control over a significant portion of Mesoamerica through conquest and alliance.