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: Surgery
[{'content': 'Which is Not required for visualisation of gall bladder in oral cholecystography - \nSelect and explain. \nA. Functioning liver, B. Motor mechanisms of gall bladder, C. Patency of cystic duct, D. Ability to absorb water', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]