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
[{'content': 'Portal vein formed by the union of- \nSelect and explain. \nA. Splenic and inferior mesenteric veins, B. Splenic and superior mesenteric veins, C. Right and left hepatic veins, D. Hepatic and splenic veins', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The portal vein is formed by the union of the superior mesentric and splenic veins behind the neck of the pancreas.', 'role': 'assistant'}]