This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
Essential amino acid is 
Select and explain. 
A. Alanine, B. Serine, C. Arginine, D. Proline
C: Arginine
Answer: C: Arginine 
Explanation: A semi-essential amino acid that occurs in proteins and is involved in the urea cycle and in the synthesis of creatine. Preparations of the base or the glutamate or hydrochloride salt are used in the treatment of <a href=" and in the assessment of pituitary function.</p>Ref: Harper&;s Illustrated Biochemistry, 26th edition, page no: 237