This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Nitric Oxide synthesised from: 
Select and explain. 
A. Arginine, B. Citrulline, C. Alanine, D. Cysteine
A: Arginine
Answer: A: Arginine 
Explanation: Ans. A. ArginineSynthesis of Nitric Oxide