Final answer:
The body of rock that returns to its original shape after stress is removed is behaving elastically, consistent with Hooke's Law stating that deformation is proportional to the applied force in such cases.
Step-by-step explanation:
If a body of rock changes shape as a result of an applied stress and then regains its initial shape and volume when the stress is removed or falls to some lower value, it is behaving elastically. This is because, for small deformations, the deformation is elastic meaning the object returns to its original shape once the force is removed. Furthermore, in an elastic deformation regime, the size of the deformation is directly proportional to the force which is described by Hooke's law, F = KAL, where F is the force applied, K is the spring constant, A is the cross-sectional area, and L is the change in length.