Science ! ty : ]
according to newton's second law of motion, if a rigid body of unchanging mass is observed accelerating, what must be happening?
a force is being applied to the mass
the mass must be changing.
a force was once applied, but is now not being applied.
no force was or is being applied to the mass.

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

a symbiotic relationship with the mitochondria