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': 'A freshly prepared oral rehydration solution should not be used after - \nSelect and explain. \nA. 4 hrs, B. 6 hrs, C. 12 hrs, D. 24 hrs', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]