On the Galápagos Islands, Natural Selection Pressures Maintain the Boundaries

Multiple Choice

On the Galápagos Islands, natural selection pressures maintain the boundaries between three species even though there is substantial gene flow between them. This example provides evidence that

A) neither the biological nor the ecological species concept applies to all situations.
B) multiple genes influence beak size.
C) these three species should be classified as a single species.
D) the medium ground finch (Geospiza fortis) has the optimal beak size.