The statement that correctly compares competing theories on Mayan civilization’s collapse is: "The overpopulation theory and the environmental degradation theory both explain that droughts caused famines in the classical period."
This is because both theories address the impacts of overpopulation and environmental strain, which could be exacerbated by drought leading to food shortages and famines. The other options do not accurately reflect common scholarly interpretations of these theories regarding the collapse of the Maya civilization.