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': 'What is the size of particle is rapid sand filter ? \nSelect and explain. \nA. 0 .1 mm, B. 0.2, C. 0.5, D. 0.4 to 0.7 mm', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Rapid sand filter \xa0→ 0.4 - 0.7 mm\nSlow sand filter → 0.2 - 0.3', 'role': 'assistant'}]