The correct option is B OB only
A conservative force is a force with the property that the work done in moving a particle between two points is independent of the taken path. Equivalently, if a particle travels in a closed loop, the net work done (the sum of the force acting along the path multiplied by the distance travelled) by a conservative force is zero. This happens till the particle comes back or regains shape the same way as it went. This happens till yield point, which is OB, after which it becomes plastic and doesn't regain its original form.