Carli Lloyd of the U.S. (in white) celebrates after scoring on a penalty kick Tuesday night in the Americans' 2-0 World Cup semifinal victory against Germany. Elsa/Getty Images hide caption

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September 13, 2009 photo of Andreas Lubitz, who is believed to have deliberately crashed Germanwings Flight 9525 into a mountain in southern France on March 24, 2015, killing all 150 people on board. Getty Images/Getty Images hide caption

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Japanese Prime Minister Shinzo Abe with U.S. Defense Secretary Ash Carter earlier this month in Tokyo. Abe's visit to the U.S. this week features an agreement for the Japanese military to have a more active role. Franck Robichon/AP hide caption

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A tray of sardines in Costa Mesa, California, in this November 17, 2014 photo. Plummeting sardine populations force a complete ban on sardine fishing off the U.S. West Coast for more than a year. LUCY NICHOLSON/Reuters /Landov hide caption

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Iraqi Prime Minister Haider al-Abadi and President Obama meet at the White House on Tuesday. The prime minister is visiting to discuss the fight against the self-proclaimed Islamic State. Jacquelyn Martin/AP hide caption

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Former Blackwater security guards were sentenced Monday for the shooting of dozens of Iraqi civilians in Nisour Square in Baghdad, Iraq. The square is seen here on Sept. 20, 2007, four days after the incident. Khalid Mohammed/AP hide caption

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Smoke and flames reportedly from Shiite Houthi rebels' camps rise over part of the Yemeni capital, Sanaa, on Monday. Fierce fighting has left people trapped, including U.S. citizens. Mohammed Huwais/AFP/Getty Images hide caption

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Iranian oil workers gather at an oil refinery south of the capital Tehran, Dec. 22, 2014. Iran's oil exports have been crippled by sanctions. Vahid Salemi/AP hide caption

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A Houthi Shiite fighter stands guard Thursday as people search for survivors under the rubble of houses destroyed by Saudi airstrikes near Sanaa Airport in Yemen. Hani Mohammed/AP hide caption

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Some of the artifacts that were handed over to Iraq during a ceremony Monday in Washington, D.C. Jackie Northam/NPR hide caption

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U.S. President Barack Obama, right, smiles after a group of children waved flags and flowers to cheer him during a welcome ceremony Wednesday with Chinese President Xi Jinping at the Great Hall of the People in Beijing. In a surprise agreement late Tuesday, China agreed to a first-ever target for capping its carbon emissions, while the United States pledge to cut faster than previously planned. Andy Wong/AP hide caption

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Data sources: David Ropeik/Harvard University, National Weather Service, World Health Organization, Northeastern University Laboratory for the Modeling of Biological and Socio-Technical Systems, National Geographic, United States Census Adam Cole and Ryan Kellman/NPR hide caption

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Scenes from an outbreak: Ebola survivor Dr. Kent Brantly; Texas Health Presbyterian Hospital in Dallas; A worker cleans the apartment where Ebola victim Thomas Eric Duncan stayed in Dallas; experimental vaccine; the Carnival Magic cruise ship off Cozumel, Mexico. Jessica McGowan/Getty; Mike Stone/Getty Images; Jim Young/Reuters/Landov; Steve Parsons/AP; Angel Castellanos/AP hide caption

itoggle caption Jessica McGowan/Getty; Mike Stone/Getty Images; Jim Young/Reuters/Landov; Steve Parsons/AP; Angel Castellanos/AP