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 are B cell markers, except: \nSelect and explain. \nA. CD-15, B. CD-19, C. CD-21, D. CD-24', 'role': 'user'}, {'content': 'Answer: A \nExplanation: . CD-15', 'role': 'assistant'}]