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': 'Removal of bacteria is: \nSelect and explain. \nA. Better with slow sand filter, B. Better with rapid sand filter, C. Equal with both, D. Depends on hardness of water', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]