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: Radiology
[{'content': 'The dye used for OCG is: \nSelect and explain. \nA. lopanoic acid, B. Sodium diatrozite, C. Biligraffin, D. Meglumine iodothalamate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. lopanoic acid', 'role': 'assistant'}]