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 chemical used to etch enamel is: 
Select and explain. 
A. Zinc oxide, B. Methyl methacrylate, C. Phosphoric acid, D. Eugenol
C: Phosphoric acid
Answer: C: Phosphoric acid 
Explanation: Etchants are relatively strong acids (pH = 1–2) used to remove smear layers and to dissolve the mineral phase to allow formation of micromechanical interlocking in enamel and in dentin. A number of acidic agents have been used to produce the required microporosity. However, phosphoric acid at a concentration between 30% and 50%, typically 37%, is the preferred etching agent to produce consistent etching patterns while not damaging the pulp.
Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, 12th ed page no 262