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
The first reference to mouth wash used for the treatment of disease of the gum is 
Select and explain. 
A. saline gargle, B. hexidine, C. Listerine, D. Urine of a child
C: Listerine
Answer: C: Listerine 
Explanation: None