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': 'The exact part of the antigen that reacts with the immune system is called as: \nSelect and explain. \nA. Clone, B. Epitope, C. Idiotope, D. Effector', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Epitope(Ref: Ananthanarayan, 9th/e, p. 88 and 7th/e, p. 81; Harrison, 18th/e, p. 2673 and 17th/e, p. 2036)* The part of the antibody or T cell receptor that interact with the epitope.", 'role': 'assistant'}]