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': 'Self etching primers \nSelect and explain. \nA. Simultaneously etch and prime dentin and enamel, B. Etches enamel only, C. Only bonds to enamel, D. Only removes smear layer', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]