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
[{'content': 'C3b is converted to C3 convertase by- \nSelect and explain. \nA. Factor B, B. Factor P, C. Factor H, D. Factor I', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Factor B", 'role': 'assistant'}]