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': 'In the pathogenesis of otosclerosis, the disease process starts in: \nSelect and explain. \nA. Periosteal layer of otic capsule, B. Endosteal layer of otic capsule, C. Bone of otic capsule which develops from cartilage, D. Mucoperiosteum of the promontory', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Otic capsule (also called bony labyrinth) has three layers: outer periosteal, inner endosteal and the middle bony. The bony layer which develops from cartilage and for some unknown reason bone of the otic capsule is absorbed and replaced by spongy vascular bone which later becomes sclerotic due to deposition of calcium.', 'role': 'assistant'}]