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
Portal vein formed by the union of- 
Select and explain. 
A. Splenic and inferior mesenteric veins, B. Splenic and superior mesenteric veins, C. Right and left hepatic veins, D. Hepatic and splenic veins
B: Splenic and superior mesenteric veins
Answer: B: Splenic and superior mesenteric veins 
Explanation: The portal vein is formed by the union of the superior mesentric and splenic veins behind the neck of the pancreas.