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 instrument does not have 4 digits? 
Select and explain. 
A. GMT, B. Excavators, C. Enamel hatchet, D. None
C: Enamel hatchet
Answer: C: Enamel hatchet 
Explanation: Three-Number Formula

It is used for the instruments in which cutting edge is at right angle to the long axis of the blade.

Eg: Enamel hatchet
Four-Number Formula

It is used for the instruments in which primary cutting edge is not at right angle to long axis of the blade.

Eg: GMT, excavators