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': 'Flux used in stainless steel solder are all except \nSelect and explain. \nA. Borax, B. Boric acid, C. Potassium fluoride, D. Sodium fluoride', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]