A security guard walks past a giant Doctor Who poster at the “Doctor Who 50th Celebration” event in the ExCeL centre on November 22, 2013 in London, England. The sold-out three day event in the ExCeL London convention centre celebrates 50 years of the show which has seen 11 actors play the role of Doctor Who and receives a worldwide cult following. (Photo by Oli Scarff/Getty Images)

Handout picture released by Telam showing the tarmac of the Pedro Palacios Avenue in Ramos Mejia, province of Buenos Aires, Argentina, under which the channeled waters of the Maldonado stream flow, after it collapsed on April 8, 2014 leaving a 40-metre-long, 1.4-metre-deep hole. About 3000 people had to be evacuated in the Argentine provinces of Neuquen (soutwest), Catamarca (northwest), Santiago del estero (center) and Cordoba (center)due to the foods caused by heavy rain, official sources said. (Photo by Daniel Dabove/AFP Photo)

A fighter jet flies above as Ukrainian soldiers sit on an armoured personnel carrier in Kramatorsk, in eastern Ukraine April 16, 2014. Ukrainian government forces and separatist pro-Russian militia staged rival shows of force in eastern Ukraine on Wednesday amid escalating rhetoric on the eve of crucial four-power talks in Geneva on the former Soviet country's future. (Photo by Marko Djurica/Reuters)

A handout photograph provided by Brian Kubicki of Costa Rican Amphibian Research Center on 26 April 2016 shows a “Crystal frog”, Hyalinobatrachium dianae (H. diane). This frog was discovered by US biologist Brian Kubicki and Costa Ricans Stanley Salazar and Robert Puschendorf in a rainy forest of Costa Rican caribbean after 40 years without notice of any new example of this kind. (Photo by Brian Kubicki/EPA/Costa Rican Amphibian Research Center)

A selection of hand-made leis, traditional Hawaiian necklaces made of flowers and worn mostly on special occasions, fill a cooler at Lin's Lei Shop in the Chinatown district of Honolulu, Hawaii December 22, 2015. Hawaii, whose economy depends heavily on tourism, sees a brief lull in visitors each year in January and February. But in addition to the usual tourist destinations, the state shows a unique overlay of mainland U.S. culture atop tropical beauty year-round. (Photo by Jonathan Ernst/Reuters)

Labourers pour molten iron into a container at a foundry in Xiangfan, Hubei province in this July 2, 2010 file photo. Iron ore is enjoying its biggest rally in years, outpacing copper and oil so far in 2016, but still weak forward prices show it may be tough to stretch the bullish outlook. Improving steel prices in top market China are helping fuel iron ore's climb as producers gear up for a seasonal uptick in demand. Yet there is no shortage of doubters who see gains in the bulk commodity as fleeting given a large glut and challenges for China's economy. (Photo by Reuters/Stringer)

This April 9, 2016 photo provided by Bertrand Piccard via Global Newsroom shows Piccard taking a selfie on board Solar Impulse 2 during a test flight over the Pacific Ocean. The solar-powered airplane on an around-the-world journey had traveled 80 percent of the way from Hawaii to California by Saturday, April 23. The aircraft's destination on this leg of the journey is Mountain View, Calif., at the southern end of San Francisco Bay. (Photo by Bertrand Piccard/Global Newsroom via AP Photo)

An elephant eats a snack after performing at Ringling Bros and Barnum & Bailey Circus' “Circus Extreme” show at the Mohegan Sun Arena at Casey Plaza in Wilkes-Barre, Pennsylvania, U.S., April 29, 2016. Elephants take a final bow at Ringling Bros and Barnum & Bailey Circus on Sunday, ending a 145-year spectacle that delighted fans but enraged animal activists, who say the highly publicized retirement is not enough. (Photo by Andrew Kelly/Reuters)