AP photographer Anja Niedringhaus laughs as she attends a swimming event at the 2004 Olympic Games in Athens, August 21, 2004. Niedringhaus, a veteran Associated Press photographer who had covered wars around the world was shot dead and another reporter was wounded on April 4, 2014 when an Afghan policeman opened fire on them in eastern Afghanistan, the news agency said. (Photo by Reuters/Staff)

“The Tonight Show” host Jimmy Fallon, center, exits the water during the Chicago Polar Plunge, Sunday, March 2, 2014, in Chicago. Fallon joined Chicago Mayor Rahm Emanuel in the event. (Photo by Andrew A. Nelles/AP Photo)

A Yemeni soldier, pictured through a vehicle's windscreen, which was damaged by a bullet, gestures out of the window, in Marib, Yemen October 15, 2015. Marib is a city that is heavily armed even by the standards of Yemen, where the ready availability of weapons helped start civil war and is now preventing anyone coming out on top. Yemenis often say there are three guns for every person, a boast that has become an urgent concern in a country where the United Nations says the humanitarian situation is "critical". (Photo by Angus McDowall/Reuters)

Women play soccer as the Tungurahua volcano spews a column of ash during an eruption in Huambalo, Ecuador, Saturday, March 5, 2016. Tungurahua is 16,480 feet (5,023 meters) high and has been active since 1999. (Photo by Dolores Ochoa/AP Photo)

A man holds a cow at the cattle market in Maiduguri, Nigeria, March 9, 2016. A Nigerian government push to strangle the Boko Haram insurgency has shut down the cattle trade that sustained the city of Maiduguri, leaving many residents with no livelihood, including many of the two million people displaced by the war. In recent months the army has taken back much of the territory lost to the jihadists during the five-year insurgency. (Photo by Afolabi Sotunde/Reuters)

Athletes from Australia's Olympic team going to the 2016 Olympics in Rio present their uniforms alongside Brazilian Samba dancer Sashya Jay at an official unveiling ceremony at Sydney's Bondi Beach, March 30, 2016. (Photo by Jason Reed/Reuters)

An army tank fires during a firefight against militants linked to al Qaeda near the southern Yemeni city of Zinjibar May 30, 2012. (Photo by Reuters/Yemen's Defence Ministry)

Dhruva Aliman does a back somersault as he dismounts from a slackline on the beach at Santa Monica, California on October 19, 2014. Slackline is a balance sport where a line of webbing is adjusted at different levels of tension between two anchor points and participants (called slackers) perform tricks and stunts including somersaults. (Photo by Mark Ralston/AFP Photo)