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': 'Feature of slow filter (w.r.t. fast filter) is/are : a) Occupies less spaceb) Highly skilled operationc) Poor bacterial qualityd) Takes more time for purificatione) Size of sand is smaller \nSelect and explain. \nA. de, B. bc, C. cd, D. bd', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Slow sand filter occupies large area (more space).\nSlow and filter requires less skilled operation.\nSlow sand filter removes more bacteria and has better bacterial control (99.9-99.99%)\nSlow sand filter requires longer duration for purification.\nSize of sand is smaller (0.2-0.3 mm).', 'role': 'assistant'}]