This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostatistics, Subject name: Social & Preventive Medicine
Sampling method used in assessing immunization status of children under immunization programme is- 
Select and explain. 
A. Systemic sampling, B. Stratified sampling, C. Group sampling, D. Cluster sampling
D: Cluster sampling
Answer: D: Cluster sampling 
Explanation: <p> Cluster sampling . Reference: Simple Biostatistics by Indeayan & Indrayan,1st edition,pg no:35-36 and Methods in Biostatistics by Mahajan,7 th edition,pg no:91.