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: Dental
[{'content': 'Tempering of steel cause \nSelect and explain. \nA. increases its toughness, B. increases hardness, C. increases ductility, D. decreases its toughness', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]