This bridge works by conveying the downward pressure of gravity inward to the center of the structure — toward a central stone called the keystone — rather than straight down

• A. Arch Bridges
• B. Keystone
• C. Conveyor Bridges
• D. Combined Bridges

Answer: (B)

This describes how an arch bridge carries load. In an arch, the weight of the bridge and any load pushes along the curved shape, directing forces inward toward the center and down into the supports. This inward thrust is what locks the structure together and lets it transfer the load to the abutments without simply pushing straight downward. The central wedge at the top—the keystone—holds the individual stones (voussoirs) in compression, so the arch remains stable and can carry loads. While the keystone is crucial, it’s a component of an arch, not the type of bridge itself; the overall mechanism described—load transfer through a curved, compression-based path to the supports—fits arch bridges best.