Urea:
a. is formed mainly in the hepatic cells of the liver.
b. is derived primarily from amine groups during the catabolism of proteins.
c. is passively reabsorbed by the kidney
d. increases in concentration as the glomerular filtrate passes down the nephron
e. excretion is via an atp dependent transport protein.

A

Explanation:

Urea is formed in the lever .Amino acid breaks down by liver due to this is formed.Urea is toxic substance and we have to remove it from our body in proper time interval.Our lever have enzymes which covert amino acid into urea then it transfer by kidney to the urine.After that it comes out from our body.

So the option A is correct.

the answer to your question is b

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.