One of the most important causes for the fall of the Maya was the presence of widespread drought in the region. Mayan religion depicts the leader of a city-state as having a direct connection to the gods and, as such, that leader is responsible for the well-being of the people. However, a long period of drought strained this concept of kingship. Instead of being able to provide, leaders found their people starving due to drought and the people began to doubt and question their leaders' rule. In that sense, the droughts in Mesoamerica were the prime cause of the civil strife that impacted the fall of the Mayan city-states.
Both B and D took place, but if you had to choose one, it would be B. The technological advances made farming much more quicker and easier for a large piece of land.
I think one way the British attempted to take control of the India subcontinent was that they removed India from a British company and placed it in the hands of Queen Victoria, who took it over.
