After Reading the Paragraph Below, Answer the Questions That Follow

After reading the paragraph below, answer the questions that follow.
In the North Pacific Ocean, two groups of the same species of killer whales (Orcinus orca) appear to be forming two different species based on what they eat. One group eats fish and the other eats mammals such as seals. Scientists can tell what they eat based on their teeth, because whales that feed on fish have significantly different wear patterns.
-One of the finest available sequences of fossils shows how horses have changed slowly and by subtle steps from small shrub-browsing ancestors to the large, grass-grazing modern horse. A large number of fossil species have been named, and it is often difficult to decide on the identity of a fossil horse because transitional forms are common. The species concept most applicable to these organisms would be

A) the biological species concept.
B) the ecological species concept.
C) the morphological species concept.
D) the phylogenetic species concept.