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': 'Insecticide of choice to prevent kala-azar- \nSelect and explain. \nA. DDT, B. HCH, C. Malathione, D. Paris green', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., DDT * Resistance to DDT has not been demonstrated in sandflies* A single application of DDT or lindane has been found effective in reducing sandflies.* DDT residue may remain effective for a period of 1 to 2 years and lindane only for a period of 3 months.", 'role': 'assistant'}]