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': 'Membrane attack complex (MAC) in complement system is: \nSelect and explain. \nA. C3b, B. C13, C. C5_9, D. C24', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. c. C5_9', 'role': 'assistant'}]