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
The following are all residual insecticides except- 
Select and explain. 
A. Pyrettmim, B. DDT, C. Gamma HHC, D. Malathion
A: Pyrettmim
Answer: A: Pyrettmim 
Explanation: Ans. is 'a' i.e., Pyrethrum