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
During activation of a scaling instrument, the facial
surface of the blade and the tooth surface should form an angle of 
Select and explain. 
A. > 15 but < 45, B. > 30 but < 60, C. > 45 but < 90, D. 90 but < 180
C: > 45 but < 90
Answer: C: > 45 but < 90 
Explanation: None