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
One of the following adjunctive aids, necessary to check
on the efficacy of oral prophylaxis for young patient 
Select and explain. 
A. Disclosing solution, B. Sandpaper strip, C. Synder test, D. Unwaxed floss
A: Disclosing solution
Answer: A: Disclosing solution 
Explanation: None