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
[{'content': 'Immunoglobulin changes in variable region - \nSelect and explain. \nA. Idiotype, B. Isotype, C. Allotype, D. Epitope', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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', 'role': 'assistant'}]