Read the Scenario and Answer the Accompanying Questions

Read the scenario and answer the accompanying questions.
In the late 1800s the federal government began eradicating the grey wolf from Yellowstone because of fear that the wolf population would have a negative impact on the area's elk, which were considered a more desirable species at that time. The eradication of this keystone species continued until the 1930s, when wolves were effectively eliminated from the lower 48 states. In the absence of wolves, elk populations begin to explode and that, in turn, resulted in what has become known as a trophic cascade. Use this information to answer the following questions on the effects of keystone species eradication and the resulting trophic cascade.
-What was the primary reason that the beaver and songbird populations were also diminished from the area?

A) The elk population was feeding on the beaver and songbirds.
B) The plants that the beaver and songbirds ate were diminishing, because of the elk's increased herbivore pressure.
C) The rivers were full of sediment, making it difficult for beaver to swim and songbirds to drink water.
D) The temperatures in the area were warming, making it difficult for the beavers and songbirds to survive in warmer weather.
E) The wolf population was feeding on the beaver and songbirds.