which material is most likely to be flexible, lightweight, and efficiently and inexpensively…

Brief Explanations:

Cellulose is a rigid plant - based material. Silk is a natural fiber, relatively expensive to produce. Starch is a polysaccharide and not typically known for flexibility in the context of materials with these properties. Polyethylene is a common plastic, which is flexible, lightweight, and can be produced efficiently and inexpensively through polymerization processes.

Answer:

B. polyethylene