This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: general microbiology, Subject name: Microbiology
Bacterial indicator for dry heat sterilization is ? 
Select and explain. 
A. Bacillus subtilis, B. Bacillus pumilis, C. Bacillus stearothermophilus, D. Coxiella burnetti
A: Bacillus subtilis
Answer: A: Bacillus subtilis 
Explanation: sterilization control Biological; the spore of a nontoxigenic strain of Clostridium tetani Bacillus subtilus subsp.niger are used microbiological test of dry heat efficacy REF:Ananthanarayan & Panicker's Textbook of Microbiology 9th edition pg no:30