This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
All of the following are essential amino acids include all, EXCEPT: 
Select and explain. 
A. Valine, B. Methionine, C. Lysine, D. Alanine
D: Alanine
Answer: D: Alanine 
Explanation: The essential amino acids are leucine, isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and histidine. Protein is required for growth and for maintenance of body structure and function. The true requirement is for nine essential amino acids plus additional nitrogen for protein synthesis. Adequate protein must be consumed each day to replace essential amino acids lost through protein turnover. Allowing for differences in protein quality and utilization and for individual variability, the RDA (USA) for protein is 56 g/d for men and 45 g/d for women. Ref: Baron R.B. (2013). Chapter 29. Nutritional Disorders. In M.A. Papadakis, S.J. McPhee, M.W. Rabow (Eds), CURRENT Medical Diagnosis & Treatment 2013.