Answer:
Option: A. Mexico's indigenous population decreased by about 20 million people by the end of the sixteenth century.
Step-by-step explanation:
Spanish invaded Mexico after defeating the Aztec Empire in 1519. Hernan Cortes, Spanish conquistador, lead an expedition which helped the Spanish to conquer the empire by killing thousands in war. The Aztecs also died by getting exposed to diseases that the Spanish brought such as smallpox, measles, malaria, typhus, and cholera. The population of indigenous people decreased by the end of the 16th century.