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': 'Not a predisposing factor for Ca esophagus: \nSelect and explain. \nA. Diverticula, B. Human papilloma virus, C. Mediastinal fibrosis, D. Caustic ingestion', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]