This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cells and Tissues of Immune System, Subject name: Pathology
CD4 is a marker for? 
Select and explain. 
A. Stem cells, B. All leukocytes, C. B - cells, D. T - cells
D: T - cells
Answer: D: T - cells 
Explanation: Ans. is 'd' i.e., T - cells o See above explanation.