This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'Smallest unit of antigenicity \nSelect and explain. \nA. Epitope, B. Paratope, C. Idiotype, D. Hapten', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Epitope of antigenic determinant is the smallest unit of antigenicity.', 'role': 'assistant'}]