a) Cellular plastics
b) Polyplastics
c) Thermoplastics
d) Artificial plastics

Answer: a
Explanation: Cellular plastics are defined as plastics whose apparent density is decreased substantially by the presence of numerous cells dispersed throughout their mass. The terms foamed plastic, expanded plastic and plastic foam are also used for cellular plastics. They have desirable properties such as, high strength-to- weight ratio and good insulating and cushioning properties.