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
Which of the following is not an instrument grasp during scaling procedure? 
Select and explain. 
A. Pen grasp, B. Thumb grasp, C. Modified pen grasp, D. Palm and thumbgrasp
B: Thumb grasp
Answer: B: Thumb grasp 
Explanation: None