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: ENT
[{'content': 'Commonest site of otosclerosis is - \nSelect and explain. \nA. Round window, B. Oval window, C. Utricle, D. Ossicles', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]