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 lactobacillus count test to assess caries activity was given by: 
Select and explain. 
A. Snyder, B. Jay, C. Hadley, D. Edelstein
C: Hadley
Answer: C: Hadley 
Explanation: LACTOBACILLUS COLONY COUNT TEST

This caries activity test was introduced by Hadley in 1933.

Essentials of preventive and community dentistry 
Soben Peter 
5th edition