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': 'Hardness of water is contributed by following salts except - \nSelect and explain. \nA. Calcium gluconate, B. Magnesium chloride, C. Calcium sulfate, D. Magnisium bicarbonate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The hardness of water is caused mainly by four dissolved compounds.These are Calcium bicarbonate Magnesium bicarbonate Calcium sulphate Magnesium sulphate Presence of any of these salt produces hardness (refer pgno:727 park 23rd edition)', 'role': 'assistant'}]