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
Sterilization accuracy is assessed by using: 
Select and explain. 
A. Clostridium perfringenes, B. Geobacillus stereothermophilus, C. Staphylococcus aureus, D. Clostridium botulinum
B: Geobacillus stereothermophilus
Answer: B: Geobacillus stereothermophilus 
Explanation: Geobacillus stereothermophilus and Bacillus subtilis subsp. Niger are used as biological indicators in sterilization.