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
Focal length of head mirror used in ENT-OPD: 
Select and explain. 
A. 9 inch, B. 10 inch (25 cm), C. 11 inch, D. 12 inch
B: 10 inch (25 cm)
Answer: B: 10 inch (25 cm) 
Explanation: Ans. is b i.e. 10 inch (25 cm)