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Work continues on the core of 1 World Trade Center (BOTTOM R), the Freedom Tower, which is being constructed at ground zero February 11, 2009 in New York City. Many September 11 first responders who became sick after working at the World Trade Center were found to have lung problems years later in a recent study. The National September 11 Memorial & Museum is expected to be completely finished in 2011. (Photo by Mario Tama/Getty Images)

27/03/09