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: Surgery
[{'content': 'What should be the density of microfilaria in blood to make it infective to the vector \nSelect and explain. \nA. 5 microfilaria / drop of blood, B. 10 microfilaria / drop of blood, C. 15 microfilaria / drop of blood, D. 20 microfilaria / drop of blood', 'role': 'user'}, {'content': 'Answer: C \nExplanation: A density of 15 microfilaria / drop of blood are needed to make it infective.', 'role': 'assistant'}]