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': 'A malarial survey is conducted in 50 villages having a population of 1 lakh. Out of 20000 slides examined,500 turned out to be malaria positive. The annual parasite incidence is \nSelect and explain. \nA. 5, B. 20, C. 0.5, D. 0.4', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]