What is a primary function of an arch bridge design?

Answer: B — To resist axial compression

An arch bridge design primarily functions to resist axial compression. The unique shape of an arch effectively converts the loads applied to it into compressive forces that are directed along the curve of the arch down to the supports at each end. This means that instead of bending or buckling under the load, the arch distributes the forces through compression, making it an efficient structure for carrying heavy loads over spans. While distributing lateral forces, providing flexibility, and supporting greater lengths are functions that can be associated with different bridge designs or other structural elements, they are not the primary purpose of an arch. The strength derived from the arch's shape is what enables it to span substantial distances, thus making the resisting of axial compression its defining characteristic and main function.