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': 'Drawback of ozone as water disinfectant is \nSelect and explain. \nA. No virucidal effect, B. Long time period for action, C. Teratogenicity, D. No residual action', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]