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 isotype class switching is determined by - \nSelect and explain. \nA. Constant region of light chain, B. Constant region of heavy chain, C. Variable region of light chain, D. Variable region of heavy chain', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Antibody genes also re-organize in a process called class switching that changes the one type of heavy chain Fc fragment to another, creating a different isotype of the antibody that retains the antigen specific variable region Ref: Ananthanarayan & Parkers textbook of microbiology 9th edition pg: 96', 'role': 'assistant'}]