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: Medicine
Which of the following is a PAN B lymphocyte.marker - 
Select and explain. 
A. CD 19, B. CD 5, C. CD 10, D. CD 38
A: CD 19
Answer: A: CD 19 
Explanation: None