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
which of the following is a essential amino acid ? 
Select and explain. 
A. Lysine, B. Alanine, C. Asparagine, D. Glycine
A: Lysine
Answer: A: Lysine 
Explanation: Essential amino acids are tryptophan valine threonine leucine lysine phenylalanine &methionine-total 8amino acids (TV TILL 8 PM). their carbon skeleton cannot be synthesized by human beings &so preformed amino acid are to be taken in food for normal growth. Normal growth will not occur if one such amino acid is deficient in the diet. Ref: DM Vasudevan - Textbook of Biochemistry for Medical Students, 7th edition, page no: 27