23.Among the polyethylene grades the one with higher stiffness, strength and melting point is (1 Point) a. LDPE b. HDPE c. PVC 24. The manufacturing processes most important associated with "thermoplastics" are(1 Point) a. Molding b. Extrusion c. Extrusion and injection molding 25.The polymer which has high toughness and creep resistance and is used to make compact discs (CD's) is(1 Point) a. Polyethylene b. Polypropylene c. Polycarbonate 26.Cellulose as a textile fiber is called(1 Point) a. Cellophane b. Rayon c. CAB 27. Heat treatment is performed on a metallic material(1 Point) a. To change its geometry b. To alter its mechanical properties c. To modify its physical properties