The correct answer is B. The presence of different and complex societies before European contact
Explanation:
Before Europeans discovered and colonized the American continent, there were multiple native tribes in most of the regions of the continent, including Mexico territory. One of these societies was the Aztec Empire that was led by Moctezuma when the Spanish colonizer Hernán Cortés and his men arrived in this territory. Moreover, it is known before the colonization many native communities formed complex societies and experienced phenomena such as conflicts between tribes, migration, among others.
In this context, the explanation of Moctezuma to Cortés about their people not being "aborigines" most likely refers that before the arrival of Cortés there were different complex societies and the Mexicans were not the first ones to live in that region or they likely originated in a different region. This makes B the correct answer.