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': 'The number of independent members in the sample is: \nSelect and explain. \nA. Null, B. Degree of freedom, C. Bias, D. Significance', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]