This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
[{'content': 'Maximum hearing loss is caused by \nSelect and explain. \nA. Ossicular chain damage, B. Tympanic membrane perforation, C. Obliteration of oval window, D. Blockage of ear canal', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 1. Complete obstruction of ear canal: 30 dB 2. Perforation of tympanic membrane. (It varies and is directly propoional to the size of perforation): 10-40 dB 3. Ossicular interruption with intact drum: 54 dB 4. Ossicular interruption with perforation: 38 dB 5. Malleus fixation: 10-25 dB 6. Closure of oval window: 60 dB Ref: Dhingra 7e pg 31.', 'role': 'assistant'}]