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 modulus of elasticity is defined as: 
Select and explain. 
A. The stress at the proportional Limit, B. The strain at the proportional limit, C. The stress to strain ratio within the proportional limit, D. None of the above
C: The stress to strain ratio within the proportional limit
Answer: C: The stress to strain ratio within the proportional limit 
Explanation: Modulus OF Elasticity
It is also referred to as 'elastic modulus' or 'Young's modulus'. It represents the relative stiffness or dity of the material within the elastic range. Young's modulus is the ratio of stress to strain. Since stress is proportional to strain (up to the proportional limit), the stress to strain ratio would be constant.
Modulus of elasticity
or
Young's modulus