selectivley permeable barrier that is made up of phospholiod bi-layer that controls what enters and leaves the cell

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands

what is this saying?

i think the answer is c hope this