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': 'Which is used for etching porcelain? \nSelect and explain. \nA. 9.6% HF, B. 1.23% HF, C. 37% HF, D. 4% HF', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]