While you are waiting to begin a foot race, you can feel your heart rate go up. this is the at work.

a. sympathetic nervous system
b. parasympathetic nervous system
c. endocrine system
d. central nervous system

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

age range would be the answer