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': 'Biological indicator for Autoclave is \nSelect and explain. \nA. CL tetani, B. Bacillus subtilis, C. Bacillus pumilis, D. Geo bacillus stearothermophilus', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Autoclave\xa0 - Geobacillus stearothermophilus\nHot air oven - CL tetani or bacillus subtilis\nIonizing radiation - Bacillus pumilus.', 'role': 'assistant'}]