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: Pathology
[{'content': 'Which is the most potent chemotactic complement? \nSelect and explain. \nA. C5b, B. C5a, C. C4a, D. C2b', 'role': 'user'}, {'content': 'Answer: B \nExplanation: C5a, C3a, C4a are chemotactic, C5a is most potent chemotactic.', 'role': 'assistant'}]