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
Efficiency of carbide bur increases by 
Select and explain. 
A. Negative (or) Zero rake angle, B. 90° edge angle, C. At high speed, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None