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': 'The difference between gram + ve and gram -ve organism is that Gram +ve org. contains - \nSelect and explain. \nA. Teichoic acid, B. Muramic acid, C. N-Acetylneuraminic acid, D. Aromatic amino acids', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Comparison of cell walls of Gram-positive and Gram-negative bacteria', 'role': 'assistant'}]