Secretary of State Hillary Clinton testifies in January 2013 before the Senate Foreign Relations Committee on the attack on the U.S. mission in Benghazi, Libya. Mandel Ngan/AFP/Getty Images hide caption

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Zachary Gallegos, 23, stands guard outside the Armed Services Recruiting Center on Thursday in Sioux Falls, South Dakota. The Pentagon has asked such self-appointed "armed citizens" to leave, citing security concerns. Kevin Burbach/AP hide caption

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An elephant in South African offers an up-close glimpse of its prodigious instrument. According to Sean Hensman of Adventures with Elephants, trunks like this one could help the U.S. Army develop a better landmine sensor. Greatstock/Barcroft Media/Barcroft Media/Landov hide caption

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A U.S. Air Force plane takes off as a Turkish air force fighter jet taxis at the Incirlik airbase, southern Turkey, in 2013. Reversing an earlier policy, Ankara has agreed to allow the U.S.-led coalition to fly anti-ISIS airstrikes from the base. Vadim Ghirda/AP hide caption

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