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': 'In the given data, degree of freedom will be -\n\xa0Duration of developing AIDSBlood Group\xa0AB\xa0C\xa0D\xa00-10 years20\xa030\xa048\xa0710-20 years\xa0100\xa015\xa038\xa010\xa020-30 years\xa012\xa09\xa08\xa03 \nSelect and explain. \nA. 12, B. 6, C. 9, D. 20', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]