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
Biological indicator for Autoclave is 
Select and explain. 
A. CL tetani, B. Bacillus subtilis, C. Bacillus pumilis, D. Geo bacillus stearothermophilus
D: Geo bacillus stearothermophilus
Answer: D: Geo bacillus stearothermophilus 
Explanation: Autoclave  - Geobacillus stearothermophilus
Hot air oven - CL tetani or bacillus subtilis
Ionizing radiation - Bacillus pumilus.