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': 'True about nitric oxide: \nSelect and explain. \nA. Free radical, B. Vasodilator, C. Oxidizing agent, D. All', 'role': 'user'}, {'content': 'Answer: D \nExplanation: A i.e. Free radical; B i.e. Vasodilator; C i.e. Oxidizing agent', 'role': 'assistant'}]