This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hepatobiliary System, Subject name: Anatomy
Portal Vein is formed by the union of? 
Select and explain. 
A. Superior Mesenteric and Inferior Mesenteric Veins, B. Superior Mesenteric and Splenic Veins, C. Superior Mesenteric And left renal vein, D. Inferior Mesenteric and Splenic Vein
B: Superior Mesenteric and Splenic Veins
Answer: B: Superior Mesenteric and Splenic Veins 
Explanation: ANSWER: (B) Superior Mesenteric and Splenic VeinsREF: Keith L. Moore 4th edition page 142-143"The hepatic portal vein, formed by the union of the superior mesenteric and splenic veins, is the main channel of the portal venous system, which collects blood from the abdominal part of the alimentary tract, pancreas, spleen, and most of the gallbladder and carries it to the liver"Major Vessels of the Hepatic Portal System