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
Drawback of ozone as water disinfectant is 
Select and explain. 
A. No virucidal effect, B. Long time period for action, C. Teratogenicity, D. No residual action
D: No residual action
Answer: D: No residual action 
Explanation: None