Which building material product innovation most dramatically transformed architectural possibilities in the 20th century?

Throughout history, architectural innovation has been driven by breakthroughs in building materials. These products have enabled architects to push boundaries, create previously impossible structures, and redefine what buildings can be. This trivia tests your knowledge of how specific product innovations have transformed architectural design and practice. Can you identify which revolutionary material had the most profound impact on 20th century architectural possibilities?

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Reinforced concrete (ferro-concrete) - allowing for cantilevers, thin shells, and unprecedented spans
Float glass - enabling the production of perfectly flat, distortion-free glass panels for curtain walls
Structural silicone sealants - permitting the development of point-fixed glass facades
Laminated timber products - creating sustainable alternatives to steel in large-span structures