A woman wearing leggings with the colours of the US flag walks along a street of Havana on February 18, 2015. President Barack Obama announced Thursday he will make a landmark visit to Cuba on March 21-22, pledging to address human rights as America pursues a historic thaw with its former Cold War foe. (Photo by Yamil Lage/AFP Photo)

Elephants feast on fruits and vegetables during the elephant buffet prior to the start of the 2016 King's Cup Elephant Polo event in Bangkok, Thailand, 10 March 2016. The annual charity event, now in its 14th edition, runs until 13 March and will involve 18 elephants brought from tourist trekking camps in Pattaya as well as some unemployed in Surin. A total of 10 teams encompassing over 40 players will take part in the event directed at raising funds to improve the lives of elephants and elephant conservation. (Photo by Diego Azubel/EPA)

A 20 metre high spiral staircase in a tower used as an emergency exit, is seen inside a Federal Reserve bank (Bundesbank) bunker, prior to the bunker's official opening to the public in Cochem, Germany, March 18, 2016. West Germany's Central Bank (Deutsche Bundesbank) stored some 20 billion German marks of emergency notes in two underground bunkers, one in Frankfurt the other in Cochem, between 1964-1988 during the cold war. (Photo by Kai Pfaffenbach/Reuters)

Justin Nelzen, in red vest, joins others as they work to rescue up to 70 horses along Cypresswood Drive near Humble along Cypress Creek, Monday, April 18, 2016, in Houston. More than a foot of rain fell Monday in parts of Houston, submerging scores of subdivisions and several major interstate highways, forcing the closure of schools and knocking out power to thousands of residents who were urged to shelter in place. (Photo by Mark Mulligan/Houston Chronicle via AP Photo)

Participants wearing superhero costumes attend the World DC Comics Super Heroes event in San Martin de Valdeiglesias, near Madrid, April 18, 2015. To celebrate the anniversary of the publication of the very first Superman story, DC Comics are asking fans to help set a new world record for the largest global gathering of people dressed as DC Comics Super Heroes. (Photo by Andrea Comas/Reuters)

A Utah Valley University student walks down the bright green lanes painted on the stairs from the gym Thursday, June 18, 2015, at Utah Valley University, in Orem, Utah. Utah Valley University spokeswoman Melinda Colton said the green lanes were intended as a lighthearted way to brighten up the space and get students attention. (AP Photo/Rick Bowmer)

Abandoned cars are seen around a cross in the village of Tbeti near Tskhinvali, the capital of the breakaway region of South Ossetia, Georgia, July 4, 2015. President Vladimir Putin signed a treaty with Georgia's rebel South Ossetia region on March 18 that almost completely integrates it with Russia, alarming Georgia and the West a year after Moscow took over Crimea. Russia won a five-day war with Georgia in 2008 over the fate of South Ossetia and another rebel region, Abkhazia. It formally recognizes both regions as independent states and signed a similar treaty with Abkhazia last year. (Photo by Kazbek Basaev/Reuters)

Ants carry a leaf with a slogan reading “Merkel, Help!”, a reference of German Chancellor Angela Merkel, at the zoo in Cologne, Germany August 18, 2015. Some of the zoo's 500,000 leaf-cutting ants carry laser-cut leaves with slogans during a campaign to protect the Amazon rain forest, organised by the German branch of World Wild Fund for Nature (WWF) and Cologne Zoo. Picture taken through the glass of the display case. (Photo by Ina Fassbender/Reuters)