The correct answer is: B. Does not show definite yield point but yield point is defined by 0.1% proof stress
A stress-strain curve is a graph that shows the relationship between stress and strain for a material. Stress is the force per unit area acting on a material, and strain is the deformation of the material per unit length.
The stress-strain curve for high tensile steel is shown below.
As you can see, the curve does not have a definite yield point. This is because high tensile steel is a ductile material, which means that it can deform plastically without breaking. The yield point is the point at which the material begins to deform plastically.
In the case of high tensile steel, the yield point is not clearly defined. This is because the material deforms plastically very gradually. As a result, the yield point is often defined as the point at which the material has undergone a 0.1% strain.
The proof stress is the stress at which the material has undergone a specified strain. In the case of high tensile steel, the proof stress is often defined as the stress at which the material has undergone a 0.1% strain.
The proof stress is a useful value to know because it is a measure of the strength of the material. The higher the proof stress, the stronger the material.
I hope this explanation is helpful. Let me know if you have any other questions.