Answer:
Vestigial structures do not have a function, yet they are homologous to functional structures in related species. They are important because they provide clues to the ancestry of the organism. Many species look similar as embryos.
DNA probably. It might be one of the latter rungs too, thymine, and 2 others I forgot
The correct order that oxygen enters the body is definitely C.
Bronchi, then Lungs, bronchioles, alveoli, blood!
Good luck!!
Atom, cell, tissue, organ
