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 Chiary 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: Answer is C (Paroxysmal nocturnal hemoglobinuria): The most common cause of hepatic vein thrombosis from the list mentioned in Harrison is Paroxysmal nocturnal hemoglobinuria, and hence is the answer of choice here.', 'role': 'assistant'}]