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
Which of the following is true regarding sampling? 
Select and explain. 
A. In simple random sampling the population is divided into strata, B. Snowball sampling is used for hidden population, C. Snowball sampling is used for hidden population More sample in systemic random sampling, D. Cluster sampling is less cost effective
B: Snowball sampling is used for hidden population
Answer: B: Snowball sampling is used for hidden population 
Explanation: Cluster sampling is cost effective. In stratified random sampling the population is divided into strata. Ref: Park, 20th Edition, Page 752