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
[{'content': 'The chemical used to etch enamel is: \nSelect and explain. \nA. Zinc oxide, B. Methyl methacrylate, C. Phosphoric acid, D. Eugenol', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 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.\nReference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, 12th ed page no 262', 'role': 'assistant'}]