the mayan aztec and inca civilizations existed for hundreds of years separated by physical features and cultural lines. What caused the fall of these ancient civilizations?

A Spanish Conquistadors brought disease and weapons that led to the eventual
these people groups.
B The civilizations combined peacefully to form the largest cultural group in his
C Internal fighting within each civilization caused the people to leave and dise
communities.
D The civilizations ran out of food and resources due to natural disaster an
explorers found them.