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
The instrument that has four unit formula 
Select and explain. 
A. Gingival margin trimmer, B. Enamel hatchet, C. Hoe, D. Chisel
A: Gingival margin trimmer
Answer: A: Gingival margin trimmer 
Explanation: None