Visitors look at a 18-foot-long model of the Titanic during the National Geographic's exhibition "Titanic: 100 Year Obsession" in Washington D.C., capital of the United States, April 5, 2012. One hundred years ago, on April 14, Titanic, the world's largest ship, sank after colliding with an iceberg, claiming 1,514 lives.[Photo/Xinhua]