What is a major change in historians' perspective on the Mayan civilization that has occurred in the past fifty years?

A. The Mayans were once considered an empire but now are believed to have been fully independent city-states.
B. The Mayans were previously considered extraordinarily peaceful, but much evidence of warfare has been discovered.
C. The Mayans were believed to have died out completely but have since been discovered in the rainforests of southern Mexico.
D. They were once believed to have been interested in astronomy, but historians have reinterpreted their surviving artifacts and no longer believe this to be true.