This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Water, Subject name: Social & Preventive Medicine
[{'content': 'The hardness of drinking water should be? \nSelect and explain. \nA. >3, B. <1, C. 3-Jan, D. >6', 'role': 'user'}, {'content': 'Answer: C \nExplanation: ANSWER: (C) 1-3REF: Park 20th ed p. 636Drinking water should be moderately hard. Softening of drinking water Is recommended when the hardness exceeds 3 mEq/LClassificationLevel of hardness ( mEq/L)Soft water< 1 ( < 50 mg/l)Moderately hard1-3 ( 50-150 mg/l )Hard water3-6 (150-300 mg/l)Very hard water> 6 ( > 300 mg/l)', 'role': 'assistant'}]