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
What should be the density of microfilaria in blood to make it infective to the vector 
Select and explain. 
A. 5 microfilaria / drop of blood, B. 10 microfilaria / drop of blood, C. 15 microfilaria / drop of blood, D. 20 microfilaria / drop of blood
C: 15 microfilaria / drop of blood
Answer: C: 15 microfilaria / drop of blood 
Explanation: A density of 15 microfilaria / drop of blood are needed to make it infective.