Выпишите все глаголы-сказуемые из текста Smart or shape memory materials are an invention that has changed the world of engineering. There are two types: metal alloys and plastic polymers. The metal alloys were made first and they are usually an expensive mixture of titanium and nickel.
Shape memory materials are called “smart” because they react to changes in their environment. For example, plastics that return to their original shape when the temperature changes. One use is in surgery where plastic threads “remember” the shape of a knot, react to the patient’s body temperature and make themselves into stitches.
Metal alloys that have a “memory” and can return to their original shape. They are used in medical implants that are compressed so they can be put inside the patient’s body through a small cut. The implant then expands back to its original shape. More everyday uses are for flexible spectacle frames and teeth braces. Liquid crystals that change shape and colour are used in climbing ropes.
The future of smart materials and their possible uses is limited only by human imagination.