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': 'For removal of bacteria - \nSelect and explain. \nA. Rapid sand filter is more effective, B. Slow sand filter is more effective, C. Both are equally effective, D. Rapid sand filter removes 70% bacteria', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Slow sand filters are for effective in removal of bacteria. Slow sand filters remove about 99.9- 99.99%.Rapid sand filters remove 98-99% bacterias. Slow sand filters occupy less area,operation is less skilled. Parks textbook of preventive and social medicine.K Park. Edition 23.Pg no: 714.', 'role': 'assistant'}]