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: Anatomy
The Poal vein is formed: 
Select and explain. 
A. By the superior mesenteric vein, B. By the splenic vein, C. At the level of 2nd lumbar veebra, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: All of the above