This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
C3b is converted to C3 convertase by- 
Select and explain. 
A. Factor B, B. Factor P, C. Factor H, D. Factor I
A: Factor B
Answer: A: Factor B 
Explanation: Ans. is 'a' i.e., Factor B