MacArthur Discovered That Five Species of Warblers Coexisted on Spruce

Multiple Choice

MacArthur discovered that five species of warblers coexisted on spruce trees by foraging on the same caterpillar,but in different places of the tree canopy.This is

A) an exception to the competitive exclusion principle.
B) an exception based on birds taking longer to eventually compete and eliminate competitors.
C) confirmation that all warblers were actually variations of the same species because different species couldn't coexist.
D) an example of resource partitioning.