Which of the following are correct with reference to amino acids?
a. Amphoteric in nature.
b. Are substituted methane molecules.
c. Serine is an alcoholic amino acid.
d. Amino acids never exist in zwitterionic form at any stage in living cells.
e. A dipeptide comprises of two peptide bonds between amino acids.

Options

A. a, b, c
B. a, d, e
C. b, c, d
D. a, c, d, e