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': 'Number of variable regions on each light and heavy chain of an antibody - \nSelect and explain. \nA. 1, B. 2, C. 3, D. 4', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A light chain has two successive domains: one constant domain and one variable domain. Heavy chain with one variable (VH) domain followed by a constant domain (CH) Ref: Ananthanarayan & Panikers textbook of microbiology 9th edition pg:94', 'role': 'assistant'}]