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': 'Distance of promontory from tympanic membrane - \nSelect and explain. \nA. 2mm, B. 5 mm, C. 6mm, D. 7 mm', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]