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': 'Following operations are done in case of otosclerosisa) Stapedectomyb) Fenestration c) Stapedotomyd) Sacculotomye) Mastoidectomy \nSelect and explain. \nA. ab, B. bc, C. abc, D. bcd', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]