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: Pathology
[{'content': 'Blood groups A1 and A2 differ in - \nSelect and explain. \nA. Chemical structure of antigen, B. Spatial configuration of antigen, C. Molecular groups, D. Ionic charges on surface', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A1\xa0and A2 blood groups have different glycolipid antigens on erythrocyte membrane.', 'role': 'assistant'}]