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
The marker for B lymphocyte is - 
Select and explain. 
A. CD 19, B. CD 68, C. CD 34, D. CD 4
A: CD 19
Answer: A: CD 19 
Explanation: Ans. is 'a' i.e., CD 19