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': 'Inverted fir tree appearance on gelatin stab is characteristic of ? \nSelect and explain. \nA. Mycoplasma, B. Bacillus anthracis, C. Clostridium, D. Bacteriodes', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]