Question

3 tries left
what innovation was made possible by the development of steel for a skeletal structure?
the elevator
the cantilever
the suspension bridge
the skyscraper

Explanation:

Steel skeletal structures provided the strength and stability needed to support tall buildings. Elevators were a separate innovation (though they complemented skyscrapers). Cantilevers are a structural element but not the main innovation enabled by steel skeletal structures. Suspension bridges use a different principle (cables). Skyscrapers, with their multiple floors, rely on a strong skeletal framework which steel provided.

Answer:

the skyscraper