单选题 .  ①A primary value in early twentieth-century Modernist architectural theory was that of "truth to materials", that is, it was essential that a building's design express the "natural" character of the building materials. ②This emphasis would have puzzled the architects of the Italian Renaissance (sixteenth century), a period widely regarded as the apex of architectural achievement, for Renaissance architects' designs were determined only minimally by the materials employed. ③The diversity of Italy's natural resources provided Renaissance architects with a wide variety of building materials. ④The builders of the Pitti Palace (1558-1570) used great blocks of Tuscan stone, just as Etruscans living in the same part of Italy had done some twenty centuries earlier. ⑤Had the Florentine Renaissance builders aped the Etruscan style, it might be said that their materials determined their style, since Etruscan style matched the massive, stark, solid character of the stone. ⑥But these same materials, which so suited the massive Etruscan style, were effectively used by the Florentine Renaissance to create the most delicate and graceful of styles.
    ①A similar example of identical materials used in contrasting styles characterizes the treatment of Roman travertine marble. ②When Baroque architects of seventeenth-century Rome desired a massive and solid monumental effect, they turned to travertine marble, whose "natural effect" is, indeed, that of spacious breadth and lofty, smoothly rounded surfaces. ③Yet during the Renaissance, this same material had been used against its "nature," in the Florentine tradition of sharply carved detail. ④Italian Renaissance architecture was shaped less by the "nature" of the materials at hand than by the artistic milieu of Renaissance Italy, which included painting and sculpture as well as architecture. ⑤While Roman travertine marble may have lent itself to fine carving, the Florentine passion for fine detail is no less marked in Florentine Renaissance painting than in Florentine Renaissance architecture. ⑥Similarly, in the next century, the emphasis on shading and corporeal density in Baroque painting mirrored the use of Roman travertine marble in Baroque architecture to create broad shadow and powerful masses.
    ①The ingenuity of Renaissance architects extended beyond merely using a material in a way not suggested by its outward natural appearance. ②If they conceived a design that called for a certain material either too expensive or difficult to work with, they made no scruple about imitating that material. ③Their marbles and their stones are often actually painted stucco. ④When the blocks of masonry with which they built were not in scale with the projected scheme, the real joints were concealed and false ones introduced. ⑤Nor were these practices confined, as some scholars insist, to the later and supposedly decadent phases of the art. ⑥Material, then, was utterly subservient to style.46.  The passage is primarily concerned with ______