C. a. Which descriptions about elastic deformation of materials are true: (a) Elastic recovery of material is a result of the return of inter-atomic bonds to its lowest-energy status; (b) elastic behavior only exist with materials without any crystal lattice defects; (c) once the material is plastically deformed, it will lose elasticity; (d) for materials with covalent bond, there exist a direction where resistance to elastic deformation is strongest. b. What are some of the characteristics of defects within material microstructures: (a) there are also certain level of defects for materials under regular conditions; (b) minimizing the defects can always lead to property enhancement; (c) material defects are important for the deformation characteristic of materials; (d) material defects can be utilized to improve certain functionality of materials. Which of these materials tend to fail catastrophically? (a) alumina, (b) carbon steel, (c) polypropylene, (d) gold, (e) concrete, (f) diamond.