Certain structural adaptations among the members of a population are passed on to future generations while others are not. What is the most likelyexplanation?

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

looks like the answer is     c     to me!