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': 'The hardness of Hard water (in mg/L) is \nSelect and explain. \nA. <50, B. 50-100, C. 150-300, D. >300', 'role': 'user'}, {'content': 'Answer: C \nExplanation: (PARK TB 25rd edition pg 787) Hardness is the soap destroying power of water. Level of hardness is expressed in terms of milliequivalents per litre where one milliequivalent is equal to 50mg calcium carbonate in one litre of water. The level of hardness of hard water is equal to 3-6mEq/L or 150-300 mg/L. CLASSIFICATION LEVEL OF HARDNESS (mEq./L) LEVEL OF HARDNESS (mg/L) soft water <1 <50 moderately hard 1-3 50-150 hard water 3-6 150-300 very hard >6 >300', 'role': 'assistant'}]