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 Al 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: Ans. is 'a' ie chemical structure of antigenA l and A2 blood groups have different glycolipid antigens on erythrocyte membrane.", 'role': 'assistant'}]