Which pair of statements best describes an essential amino acid?
a. It is an amino acid that contains peptide bonds. An example is proline.
b. It is an amino acid that contains nitrogen. An example is aspartic acid.
c. It is an amino acid that cannot be made by the body. It must be obtained from eating certain foods.
d. It is an amino acid that can be produced by the body. Vitamin supplements maintain healthy levels.