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': 'Human immunoglobulins are divided based on \nSelect and explain. \nA. Functional differences, B. Structural differences, C. Complement fixation, D. None of the above', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]