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
A layman before introduction of fluoride in prevention of dental caries knew about it as a constituent used in 
Select and explain. 
A. Pesticide, B. Industrial use, C. Fertilizers, D. Irrigant
A: Pesticide
Answer: A: Pesticide 
Explanation: None