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': 'Greatest stress generated in a material till it follows a directly proportional relationship \nSelect and explain. \nA. Yield Strength, B. Proportional Limit, C. Toughness, D. Ultimate strength', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]