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: Physiology
NO is synthesized by: 
Select and explain. 
A. Uracil, B. Aspaate, C. Guanosine, D. Arginine
D: Arginine
Answer: D: Arginine 
Explanation: D i.e. Arginine