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': 'Anaphylotoxin in complement system ? \nSelect and explain. \nA. C3b, B. C5_9, C. C5a, D. C1_3', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Csa", 'role': 'assistant'}]