Which of the following is not a branched-chain amino acid?

A branched-chain amino acid (BCAA) is an amino acid having aliphatic side-chains with a branch. Among the proteinogenic amino acids, there are three BCAAs: leucine, isoleucine and valine. They are among the nine essential amino acids for humans, accounting for 35% of the essential amino acids in muscle proteins and 40% of the preformed amino acids required by mammals.