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': 'Which immunoglobulin crosses placenta maximally: \nSelect and explain. \nA. IgG1, B. IgG2, C. IgG3, D. IgG4', 'role': 'user'}, {'content': 'Answer: A \nExplanation: IgG1 - max , IgG4 - minimum', 'role': 'assistant'}]