[单项选择]

DEVELOPMENTS IN THE CONSTRUCTION OF TALL BUILDINGS

1 Until the nineteenth century, most tall buildings were constructed of load-bearing masonry walls. Masonry walls had to be thick, particularly at the base, to support a building’s great weight. Stoneworkers built these walls by placing stone upon stone or brick upon brick, adding strength and stability by placing layers of mortar or cement between the stones. Floors and roofs had to be supported by wooden beams, but the major vertical force of buildings was supported by thick masonry walls. This imposed serious limitations on the number and size of windows.
2 In the 1850s, an alternative was emerging that would eliminate the need for exterior weight-bearing walls: a three-dimensional grid of metal beams and columns. The introduction of metal construction made it possible to build larger interior spaces with fewer columns than before. The new construction was capable of suppor
A. Stone floors and roofs
B. Thick walls of stone or brick
C. A large number of tall windows
D. An interior frame of metal