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