This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Basic Concepts, Subject name: Pathology
Which of the following is a pan-T lymphocyte marker? 
Select and explain. 
A. CD 2, B. CD 3, C. CD 19, D. CD 25
B: CD 3
Answer: B: CD 3 
Explanation: Antigen Designation Normal cellular distribution Primarily T-cell associated CD 1 Thymocytes and Langerhans cells CD3 Thymocytes, mature T cells CD4 Helper T cells, subset CD5 T cells and a small subset of B cells CD8 Cytotoxic T cells, subset of thymocytes, and some NK cells