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
[{'content': 'Bacterial indicator for dry heat sterilization is ? \nSelect and explain. \nA. Bacillus subtilis, B. Bacillus pumilis, C. Bacillus stearothermophilus, D. Coxiella burnetti', 'role': 'user'}, {'content': "Answer: A \nExplanation: 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", 'role': 'assistant'}]