Which Amino Acid does not have L and D configurations?

Glycine is unique among the standard amino acids because it has a hydrogen atom as its side chain (R group). The central carbon atom (α-carbon) of glycine is bonded to two hydrogen atoms, a carboxyl group (-COOH), and an amino group (-NH2). This symmetry around the α-carbon means that glycine does not have a chiral center, making it the only standard amino acid that is not optically active. Therefore, glycine does not exist in L or D configurations, unlike all other standard amino acids which have a chiral center and can exist as mirror-image forms (enantiomers) due to the presence of four different groups attached to the α-carbon. Problem: Give an answer to this question and explain: Which amino acid is not chiral and thus does not have an L or D configuration? A) Alanine B) Glycine C) Serine D) Isoleucine