What are the three main groups that Arthrodira is divided into?

A. Actinolepida, Phlyctaenii, and Eubrachythoraci
B. Actinolepida, Phlyctaenii, and Brachythoraci
C. Brachythoraci, Buchanosteoidea, and Homosteidae
D. Holonematidae, Eubrachythoraci, and Homosteidae
Answer: 