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: Medicine
[{'content': 'Commonest cause of Budd Chiari syndrome is - \nSelect and explain. \nA. Valve in the IVC, B. Hepatocellular carcinoma, C. Paroxysmal nocturnal hemoglobinuria, D. Renal cell carcinoma', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]