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: Dental
All of the following affects bur efficiency except: 
Select and explain. 
A. Spiral angle, B. Head length and diameter, C. Neck diameter, D. Crosscut
B: Head length and diameter
Answer: B: Head length and diameter 
Explanation: Taper angle and head length and diameter has no effect on bur efficiency.