Kidneys process nitrogenous wastes by

metabolic wastes result from breakdown of proteins.

d. pumping ions across membranes to separate water from waste products.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

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