The Structures of the Amino Acids Proline and Glycine Are $\alpha$

The structures of the amino acids proline and glycine are shown below. Which of the following statements is true?

A) glycine is an $\alpha$ -amino acid, but proline is not
B) both proline and glycine are chiral molecules
C) glycine is achiral and proline is chiral
D) proline exists as four enantiomers