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': 'Best diagnosis of tracheo-oesophageal fistula is by: \nSelect and explain. \nA. Barium sulphate, B. Conray 240, C. Dianosil, D. Urograffin', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Dianosil', 'role': 'assistant'}]