Question

How did plastic revolutionize the art of furniture design?

Answer 1

B. Designers could create works that were sturdy and moldable. 

I do hope this isn't from a test, if it is you should be doing your own work, but the general idea is that plastic made it easier to make decently sturdy and extremely moldable, malleable, objects. That just made collages, sculptures, and other physical artworks all that much easier to create.