How are proteins distinguished from each other?
a. by the amounts of carbon, oxygen, and hydrogen they contain
b. by the kinds of fatty acids they contain
c. by the kinds of bonds that join their monomers
d. by the order of the amino acids that form them?

Option "d" is correct. 

Proteins are known as the most complex structural molecules. Proteins constituents consist of almost 20 different types of amino acids. Each Protein has a unique structure and sequence of amino acids. This sequence of amino acids forms a long chain, and each amino acid is connected with other by a covalent bond known as peptide bond.