This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
All are essential amino acid except 
Select and explain. 
A. Phenylalanine, B. Lysine, C. Leucine, D. Glycine
D: Glycine
Answer: D: Glycine 
Explanation: The essential amino acids are Isoleucine, Leucine Threonine Lysine, Methionine, Phenylalanine, Tryptophan, and Valine.Ref: DM Vasudevan - Textbook of Biochemistry for Medical Students, 7th edition, page no: 27