A walker has left a handprint on a snow- covered tree trunk on Grosser Feldberg mountain in the Taunus mountain range, Germany, 16 January 2017. (Photo by Frank Rumpenhorst/DPA)

A man walks on a bridge crossing over the Besor stream on a rainy day, near Kibbutz Tze'elim in Israel's southern Negev desert February 16, 2017. (Photo by Amir Cohen/Reuters)

Workers lay railway track in a tunnel of the Crossrail project in Stepney, east London, Britain, November 16, 2016. Crossrail, which is Europe's largest construction project, is a railway link which will connect outlying areas to the east and west of London with tunnels under the centre of the capital. (Photo by Stefan Wermuth/Reuters)

Liu Yang, China's first female astronaut, waves during a departure ceremony at Jiuquan Satellite Launch Center, on June 16, 2012. (Photo by Jason Lee/Reuters via The Atlantic)

Surfer Hannah Cornett attends The 2014 ESPYS at Nokia Theatre L.A. Live on July 16, 2014 in Los Angeles, California. (Photo by Jason Merritt/Getty Images)

Grumpy Cat attends the “Grumpy Cat: A Grumpy Book” Book Event at Bookends Bookstore on October 16, 2013 in Ridgewood, New Jersey. (Photo by Michael N. Todaro/WireImage)

Craig Jobbins, first buyer of the new iPad to leave the Apple Store, poses for photographers in Covent Garden on March 16, 2012 in London, England. (Photo by Matthew Lloyd/Getty Images)

Children with balloons play beside the statue of British comedy legend Eric Morecambe on January 16, 2012 in Morecambe, England. According to scientists January 16, 2012 was “Blue Monday”, the most depressing day of the year. (Photo by Christopher Furlong/Getty Images)