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: Unknown
Microlaryngoscopy is usually done with an objective lens with focal length of: 
Select and explain. 
A. 200 mm, B. 400 mm, C. 100 mm, D. 300 mm
B: 400 mm
Answer: B: 400 mm 
Explanation: - Surgical microscopeshave the ability to fine focus with focal lengths that may vary from the standard microlaryngeal surgical focal length of 400 mm.