This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Which of the following is a pan T lymphocite marker - 
Select and explain. 
A. CD2, B. CD3, C. CD 19, D. CD 25
B: CD3
Answer: B: CD3 
Explanation: The TCR is a disulfide-linked membrane-anchored heterodimeric protein normally consisting of the highly variable alpha (a) and beta (b) chains expressed as pa of a complex with the invariant CD3 chain molecules. Reff: Ananthanarayanan & Panikers textbook of microbiology 9th edition pg: 133