Field Observation Suggests That Populations of a Particular Species of Herbivorous

Field observation suggests that populations of a particular species of herbivorous mammal undergo cyclic fluctuations in density at three- to five-year intervals. Which of the following represent (a) plausible explanation(s) of these cycles?

A) Periodic crowding affects the endocrine system, resulting in increased aggressiveness.
B) Increases in population density lead to increased rates of predation.
C) Increases in rates of herbivory lead to changes in the nutritive value of plants used as food.
D) Increases in population density lead to more proximal infestations of parasites to host animals.
E) All of the above are plausible explanations of population cycling.