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': 'When the level of hardness in water is around 150-300 mg / litre it is classified as \nSelect and explain. \nA. Very hard water, B. Soft water, C. Moderately hard water, D. Hard water', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]