Soviet Army soldiers sit on their tanks in front of the Czechoslovak Radio station building in central Prague during the first day of Soviet-led invasion to then Czechoslovakia on August 21, 1968. (Photo by Libor Hajsky/Reuters)

A woman walks against blowing snow in Evanston, Illinois, on February 8, 2014. (Photo by Nam Y. Huh/Associated Press)

Hotel staff practice self-defence skills after a training session given by team member of Special Weapons and Tactics (SWAT) team, in Hangzhou, Zhejiang province, April 7, 2016. (Photo by Reuters/Stringer)

Four-month-old fox cubs squaring up to each other in Walthamstow, England on August 7, 2015. (Photo by Greg Morgan/Barcroft Media)

Young gymnasts practice pull-up on a bar at a gymnasium of a sports school in Jiaxing, Zhejiang province April 11, 2015. (Photo by William Hong/Reuters)

The Chilean ship “Skorpios II” is seen after it ran aground in “Maillen” island, near Puerto Montt, south of Santiago, in this handout picture from the Chilean Navy, February 5, 2015. According to the Chilean Navy, the ship's 89 passengers and 31 crew members were all evacuated and no oil spills or casualties were reported. (Photo by Reuters/Chilean Navy)

A ring-tailed lemur is pictured at Zoom Torino, a zoological park in Cumiana near Turin, on April 22, 2015. Zoom Torino is a new immersive zoological park, where animals can be seen without bars or cages, only natural barriers ensure the visit. (Photo by Marco Bertorello/AFP Photo)

Two men play golf with a tennis ball as a snowstorm sweeps through Times Square, Tuesday, March 14, 2017, in New York. (Photo by Mark Lennihan/AP Photo)