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
The strain that occurs when a material is stressed to its proportional limit is: 
Select and explain. 
A. Resilience, B. Maximum flexibility, C. Toughness, D. Elastic limit
B: Maximum flexibility
Answer: B: Maximum flexibility 
Explanation: None