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
Strain is defined as: 
Select and explain. 
A. An applied load or force, B. A deformation resulting from an applied load, C. An external force opposing an applied load, D. An internal force opposing an applied Load
B: A deformation resulting from an applied load
Answer: B: A deformation resulting from an applied load 
Explanation: Strain—Change in dimension per unit initial dimension. For tensile and compressive strain, a change in length is measured relative to the initial reference length.
Strain, or the change in length per unit length, is the relative deformation of an object subjected to a stress. Strain may be either elastic, plastic, elastic and plastic, or viscoelastic. Elastic strain is reversible. The object fully recovers its original shape when the force is removed. 
Phillips dental materials 12th edition page no 48, 51