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': '500 people of viral fever are treated with a medicine. 80 percent were cured in 3 days. True statement about efficacy of medicine - \nSelect and explain. \nA. Medicine is effective, B. Cannot be commented, C. Medicine is ineffective, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]