After Reading the Paragraphs Below, Answer the Question(s) That Follow(s)

After reading the paragraphs below, answer the question(s) that follow(s) .
Bipedalism is one of the most important characteristics of hominin evolution. The appearance of bipedalism led to anatomical changes that are considered to be distinguishing characteristics among hominin fossils. The evidence for bipedalism is supported by fossil evidence from more than 4 million years ago and a trackway of footprints in volcanic ash 3.6 million years old.
Recently, however, scientists have focused on the link between tooth structure and diet in the evolution of the early hominins, specifically in Australopithecus species. Detailed studies of hominin dental features have provided evidence of an important dietary shift that led to adaptive radiation within this genus. Most of the evidence comes from analyses of tooth size and shape, microscopic wear patterns on teeth, and jaw structure. The evidence suggests that fibrous plant materials became more important through the Pliocene, perhaps as critical components in the diet of some species.
-In addition to the two typical embryonic layers, most animals have a third embryonic layer called the

A) ectoderm.
B) castrula.
C) mesoderm.
D) endoderm.