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
Galagan's formula is to: 
Select and explain. 
A. Measure the amount of fluoride in toothpaste, B. Measure the amounts of fluoride in drinking water, C. Calculate the fluoride concentration in drinking water depending on temperature of the area, D. Assess the age of the individual by dentition status
C: Calculate the fluoride concentration in drinking water depending on temperature of the area
Answer: C: Calculate the fluoride concentration in drinking water depending on temperature of the area 
Explanation: None