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': 'Berkesonian bias in a case control study is a bias due to: \nSelect and explain. \nA. Presence of confounding factors, B. Different admission rates for different diseases, C. Bias introduced by investigator, D. Patient can not recall or gives false information', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]