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
[{'content': 'In random sampling chance of being picked up is- \nSelect and explain. \nA. Same and known, B. Not same and not known, C. Same and not known, D. Not same but known', 'role': 'user'}, {'content': 'Answer: A \nExplanation: .', 'role': 'assistant'}]