Wolves in Yellowstone National Park Feed on Elk, Bison, and Coyotes.When

Wolves in Yellowstone National Park feed on elk, bison, and coyotes.When wolves were absent from the park, elk populations increased and browsed young aspen trees so much that they could not become established.The elk also browsed willows, which beavers required, and beavers disappeared from the area.When wolves were reintroduced into the park after many years of absence, elk declined, and aspen, willows, and beavers returned.This suggests that wolves in Yellowstone were responsible for

A) a trophic cascade.
B) decreased species diversity.
C) decreased habitat for beavers.
D) decreased reproduction of aspen trees.
E) direct control of willow and aspen populations.