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NEW YORK, NEW YORK- SEPTEMBER 11: Smoke from the burning World Trade Center towers fills up the downtown Manhattan skyline after both buildings were attacked by airplanes on September 11, 2001 in New York City. (Photo by Andrew Lichtenstein/Corbis via Getty Images)

NEW YORK, NEW YORK- SEPTEMBER 11: Smoke from the burning World Trade Center towers fills up the downtown Manhattan skyline after both buildings were attacked by airplanes on September 11, 2001 in New York City. (Photo by Andrew Lichtenstein/Corbis via Getty Images)