This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
[{'content': 'Moderately hard water has hardness level \nSelect and explain. \nA. <1, B. 3-Jan, C. 6-Mar, D. >6', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ref: 25th Ed K.Park's Textbook Of Preventive and Social Medicine Pgno : 763", 'role': 'assistant'}]