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': 'Freshly prepared ORS should be used within \nSelect and explain. \nA. 12 hours, B. 1 day, C. 2 days, D. 4 hours', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]