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: Ophthalmology
[{'content': 'Diameter of head mirror in ENT is: \nSelect and explain. \nA. 20 cm, B. 22 cm, C. 10 cm, D. 26 cm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. is c i.e. 10 cm Diameter of the head mirror used in ENT is 89 mm (3and half inch).', 'role': 'assistant'}]