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: Microbiology
[{'content': 'C\n3\n convertase acts on - \nSelect and explain. \nA. C4b2b, B. C4b2B3 a, C. C4b, D. C3', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]