If these were the missing choices:
A)Gly
B)Ala
C)Tyr
D)Asn
E)Thr
The answer is E.) Thr.
Thr stands for Threonine. It is a polar amino acid. Its side chains are also hydroxylic.
Aside from promoting normal growth by helping maintain proper protein balance in a body, Threonine also supports cardiovascular, central nervous, immune system, and liver function.