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
Immunoglobulin changes in variable region - 
Select and explain. 
A. Idiotype, B. Isotype, C. Allotype, D. Epitope
A: Idiotype
Answer: A: Idiotype 
Explanation: an idiotype is a shared characteristic between a group of immunoglobulin or T cell receptor (TCR) molecules based upon the antigen binding specificity and therefore structure of their variable region Reff: www.mayoclinic.com