Final answer:
Flying buttresses were used in Gothic architecture to support vaulted ceilings and stabilize thin walls against lateral forces, preventing structural failure.
Step-by-step explanation:
The answer to the question is (B) Flying buttresses, vault. Flying buttresses were developed during the Gothic period as a means to support the thin walls of large buildings, such as cathedrals, which were subject to lateral forces caused by the weight of the vaulted ceilings. These architectural features were crucial in redirecting the forces from pointed arches to the ground, thereby stabilizing the structure and preventing the walls from collapsing. When the construction of the Gothic-style buildings began, the slim walls started to show signs of fracturing. The implementation of flying buttresses at points of failure not only resolved this issue but also became a standard practice in the construction of tall cathedrals thereafter.