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: Dental
[{'content': 'Nalgonda technique involves addition of following chemicals: \nSelect and explain. \nA. Lime, bleaching powder, filter alum, B. Magnesia, calcium phosphate, filter alum, C. Alumina, carbon, lime, D. Sulphonated saw dust, coal, calcium phosphate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]