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
What is the most common cause for Budd chiary syndrome- 
Select and explain. 
A. Right ventricular failure, B. PNH, C. Valve in hepatic veins, D. Polycythemia vera
D: Polycythemia vera
Answer: D: Polycythemia vera 
Explanation: Answer is D (Polycythemia vera) Polycythemia vera is the most common cause for Budd chiral syndrome amongst the options provided.