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The particular innovation that allowed large-scale skyscrapers to be built was __________.
Until the late nineteenth century, buildings had serious vertical size restrictions due to the weight placed on them by bricks and other traditional materials. With the introduction of steel, an alloy of iron, new possibilities were available to builders. In particular, the use of steel-frame construction, which built a "sheet" around steel beams, allowed for buildings stretching taller than ten stories.
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The Washington Monument is a traditional memorial structure known as __________.
The Washington Monument, in the center of the National Mall in Washington, D.C., is the world's largest memorial obelisk. Obelisks, four sided pillars that originated with the ancient Egyptians, have long been used in Western culture as memorial markers. The Washington Monument was conceived in the 1840s as more than just the obelisk, but ran into funding problems and was only completed in its simpler form in 1885.
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