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: Social & Preventive Medicine
In maternal and child welfare program the sampling is done by which method? 
Select and explain. 
A. Systematic, B. Cluster-30, C. Group, D. Stratified
B: Cluster-30
Answer: B: Cluster-30 
Explanation: None