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
[{'content': 'True statements with regard to sampling-a) Snowball sampling is used for hidden populationb) More sample in systemic random samplingc) In stratified random sampling population is divided into stratad) Cluster sampling is less cost-effective \nSelect and explain. \nA. ac, B. bc, C. ad, D. b', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]