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
[{'content': 'Nitric Oxide is produced in: \nSelect and explain. \nA. Endothelium, B. Plasma, C. Platelets, D. Serum', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. Endothelium Nitric oxide is synthesized from arginine by the enzyme NO synthetase (NOS) in endothelial cellsQ. It causes vasodilation.', 'role': 'assistant'}]