ANS:D - plastic

Hot and cold working of materials primarily causes plastic deformation. When materials undergo hot or cold working processes such as forging, rolling, extrusion, or drawing, they are subjected to mechanical forces that exceed their yield strength. This results in the permanent deformation of the material, where its shape is changed without springing back to its original form once the force is removed. This type of deformation is known as plastic deformation. Viscoelastic deformation involves both elastic and viscous responses and is more characteristic of polymers and certain complex materials under certain conditions. Isotropic deformation refers to uniform deformation in all directions, which might occur in some materials but isn't specifically associated with hot or cold working processes. Elastic deformation occurs when materials are subjected to forces within their elastic limits, causing them to deform reversibly. However, hot and cold working typically involve forces that exceed the elastic limit, resulting in permanent, or plastic, deformation. Therefore, the most appropriate term to describe the deformation caused by hot and cold working of materials is plastic deformation.