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: Dental
[{'content': 'A sampling unit is defined as \nSelect and explain. \nA. A group of sample, B. A subset of sample, C. Representing every member of sample, D. All of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]