Here are the corrected answers for each question:
Question 1:
The region where the Maya lived suffered from two megadroughts.
Question 2:
foreign invasion
Question 3:
The Maya became vulnerable to climate variability.
Question 4:
The overpopulation theory and the environmental degradation theory both explain that droughts caused famines in the classical period.
Question 5:
an understanding of the types of sources used by the historian