Medical personnel work outside the medical tent in the aftermath of two explosions near the finish line of the Boston Marathon on Monday. At area hospitals, doctors say they were confronted with the kinds of injuries U.S. troops get in Iraq and Afghanistan. Elise Amendola/AP hide caption

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Workers cover an entrance with plywood at a subway station in New York City in preparation for flooding from Hurricane Sandy. Mary Altaffer/AP hide caption

itoggle caption Mary Altaffer/AP

From left: Frank Wild, Ernest Shackleton, Dr. Eric Marshall and Jameson Adams head back to base camp after getting within 97 miles of the South Pole — closer than anyone had gotten before them — in January 1909. /Getty Images hide caption

itoggle caption /Getty Images