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
According to the instrument formula given by G.V. Black, the primary cutting edge angle should be: 
Select and explain. 
A. >50 degree, B. >90 degree, C. <50 degree, D. <90 degree
A: >50 degree
Answer: A: >50 degree 
Explanation: Blade angle should be more than 50 degree.