B. is the answer i really hope i helped please mark as brainliest.
Proteins. <span>The amino acids in a polypeptide chain are linked by peptide bonds. Once linked in the </span>protein<span> chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen, and oxygen atoms are known as the main chain or </span>protein<span> backbone.</span>
Models are used to stimulate reality and make predictions
Frogs do have lungs but they are small and rarely used, frogs mostly take in moisture through the skin in process called cutaneous gas exchange.
It is called a population since they are all the same species
