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 component of the cell wall is responsible for endotoxic activity: \nSelect and explain. \nA. Region I, B. Region II, C. Region III, D. Biovin antigen', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]