This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Microbiology Pa 1 (History, Microscopy, Stains and Structure and Physiology of Bacteria), Subject name: Microbiology
[{'content': 'Longest pathogenic Bacillus species is \nSelect and explain. \nA. Bacillus subtilis, B. Bacillus cereus, C. Bacillus anthracis, D. Bacillus megaterium', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Longest pathogenic Bacillus species is Bacillus anthracis (1.2 mm width and 3-5mm long). B. anthracis causes anthrax Largest known Bacillus species is B. megaterium, (1.5 mm width and 4 mm long).', 'role': 'assistant'}]