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: Physiology
[{'content': 'The serum concentration in which of the following human IgG subclasses is maximum? \nSelect and explain. \nA. IgG1, B. IgG2, C. IgG3, D. IgG4', 'role': 'user'}, {'content': 'Answer: A \nExplanation: IgG 1 - 65%, IgG2- 23%. IgG3 -8% IgG4 - 4%', 'role': 'assistant'}]