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 water is contributed by following salts except – \nSelect and explain. \nA. Calcium gluconate, B. Magnesium chloride, C. Calcium sulfate, D. Magnisum bicarbonate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]