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 first reference to mouth wash used for the treatment of disease of the gum is \nSelect and explain. \nA. saline gargle, B. hexidine, C. Listerine, D. Urine of a child', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]