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: Surgery
[{'content': 'The substance used in OCG is - \nSelect and explain. \nA. Iapanoic acid, B. Sodium diatrozite, C. Meglumine iodothalamate, D. Biligraffin', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e. Iapanoic acid", 'role': 'assistant'}]