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': 'Hardness of drinking water should be: \nSelect and explain. \nA. Less than 1, B. 3-Jan, C. More than 3, D. More than 6', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 3-Jan', 'role': 'assistant'}]