Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

Architecture has social purposes and meets practical needs by means of combining art and technological innovations. In building construction, however, an emergence of new materials does not make its precursors obsolete, and architectural knowledge is cumulative. The fact that today much is constructed from prefabricated concrete does not do away with brick. Furthermore, despite dramatic changes and increased technological sophistication of architectural design and construction, the essential apparatus of erecting a building has remained rooted in preindustrial traditional practices passed down during the millennia. The social and utilitarian expectations of structures are largely based on elemental demands of keeping out elements and enemies, ameliorating the extremes of heat, and avoiding the instruction of wind, precipitation, and pests. Gravity, air pressure, and earthquakes can induce tensions that have to be accounted for when constructing functional enclosed space. Vertical stacking of masonry materials causes compression that can lead to important problems when a structure is spanned to build a roof and connect walls. Arches, vaults, and domes were specifically developed to alleviate the compression by directing the spanning element along a curve rather than a straight line. Building suspension structures, dams, and tunnels became possible in the nineteenth century with the increased availability of steel that could reinforce structural frames and enable them to withstand natural forces previously believed to be insurmountable.Functional evolutions of modern buildings create new demands on the analysis of structural behavior and engineering. Few occupants of skyscrapers view elevators as elaborate systems of vertical transportation. Humidity and temperature control, forced ventilation, natural and artificial lighting, sanitation and disposal of waste, electrical wiring, and fire prevention make very tall constructions engineering marvels that also must be aesthetically pleasing and physically convenient.Erecting a structure involves a great deal more than merely attending to the aesthetics and psychological experience of architectural space. The shape, size, and incombustibility of locally available construction materials fostered developments of specific technologies, and brick and stone masonry have evolved in response to the need for structural durability. Advances in civil engineering and knowledge associated with properties of building materials combine to lead to innovations in architectural design. Tools and skills required to exploit easily obtainable materials have continued to inform the development of modern industrialized technologies.

The purpose of paragraph 3 is to suggest that ________.