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': 'The optimal time and temperature required for sterilization in an autoclave is \nSelect and explain. \nA. 140°C x 2 hrs. x 10 lbs pr, B. 121°F x 15 mts. x 15 lbs pr, C. 121°C x 15 sec. x 15 lbs pr, D. 121°C x 15 mts. x 15 lbs pr', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]