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': 'Which of the following statement about DDT is false - \nSelect and explain. \nA. It is contact poison, B. Residual effect lasts for 18 months, C. immediately kills the prey, D. Permethrin has synergistic action', 'role': 'user'}, {'content': "Answer: C \nExplanation: DDT is a synthetic contact poison. It acts on the nervous system of insects. It does not cause immediate death, take several hours to kill. The residual action of DDT may last for 18 months depending on the treated surface. Has no repellent action. As residual spray, the dose is 100 -200 mg per sq.ft area. Park's Textbook of Preventive and Social Medicine, 25th Edition, Pg 833", 'role': 'assistant'}]