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': 'Valve of heister is seen in ? \nSelect and explain. \nA. Cystic duct, B. Common bile duct, C. Common hepatic duct, D. Pancreatic duct', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The mucous membrane of the cystic duct forms a series of 5-12 crescentic folds, arranged spirally to form the so called spiral valve of Heister. This is not a true valve.', 'role': 'assistant'}]