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': 'All of the following are B cell markers except: \nSelect and explain. \nA. CD 22, B. CD 19, C. CD 20, D. CD 34', 'role': 'user'}, {'content': 'Answer: D \nExplanation: CD 34', 'role': 'assistant'}]