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 sampling method used in pathfinder survey is 
Select and explain. 
A. Stratified cluster sampling, B. Simple random sampling, C. Snowball sampling, D. Two stage sampling
A: Stratified cluster sampling
Answer: A: Stratified cluster sampling 
Explanation: None