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 positive and negative bacteria lies in their \nSelect and explain. \nA. Cell wall, B. Cell membrane, C. Nuclear material, D. Mesosomes', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]