An undercover police officer, who had been marching with anti-police demonstrators, aims his gun at protesters after some in the crowd attacked him and his partner in Oakland, California December 10, 2014. Police said more than 100 demonstrators marched in Berkeley, California, which has a history of social activism. Under cloudy skies, turnout was smaller than earlier in the week, when demonstrators in the area threw rocks at police and shut down a major freeway. (Photo by Noah Berger/Reuters)

Local men help a wounded woman after a mortar attack by the Ukrainian army of the center of Donetsk, Ukraine, 14 August 2014. Reports state that ten local people where wounded and one killed after the mortar attack. (Photo by Sergei Ilnitsky/EPA)

Handout photo issued by Easyart of an experimental motorcycle as an archive of weird and wacky innovations has been unearthed by an amateur historian as he trawled through a collection of images spanning the last 100 years. (Photo by Easyart/PA Wire)

A woman cries as she stands next to house destroyed by the earthquake in the Pacific coastal town of Pedernales, Ecuador, Sunday, April 17, 2016. A magnitude-7.8 quake, the strongest since 1979, hit Ecuador flattening buildings, buckling highways along its Pacific coast and killing hundreds. (Photo by Dolores Ochoa/AP Photo)

Singer Paulina Rubio performs during the Latin Billboard Awards, Thursday, April 28, 2016 in Coral Gables, Fla. (Photo by Wilfredo Lee/AP Photo)

A country music fan cools off in the wind on the second day of the Stagecoach country music festival in Indio, California April 26, 2014. (Photo by Mike Blake/Reuters)

People walk through crop circles in a cornfield near Raisting, Germany, on July 28, 2014. According to media reports, a balloonist had discovered the circle some days ago. Since then, hundreds of people came to the field to watch it, however it is unclear who did create the pattern. (Photo by Karl-Josef Hildenbrand/DPA)

Hot air balloons take to the skies as they participate in the mass assent at sunrise on the second day of the Bristol International Balloon Fiesta on August 11, 2017 in Bristol, England. More than 130 balloons have gathered for the four day event, now in its 39th year and now one of Europe's largest annual hot air balloon events, being hosted in the city that is seen by many as the home of modern ballooning. (Photo by Matt Cardy/Getty Images)