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': 'True about valves in portal venous system - \nSelect and explain. \nA. Present at the junction of superior mesenteric artery with the splenic artery, B. Within the portal vein only, C. The whole system is valveless, D. In the intrahepatic portion of portal vein', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Although demonstrable during fetal and early neonatal period, there are no valves in a portal vein and its tributaries in the postnatal period.', 'role': 'assistant'}]