Swiss police officers stand beside of mock gates of the NEAT Gotthard Base Tunnel inside the event hall for the upcoming opening ceremony near the town of Erstfeld, Switzerland May 31, 2016. The celebrations of the opening of the Gotthard Base Tunnel will start on June 1, 2016. With a length of 57 km (35 miles) crossing the Alps, the Gotthard Base tunnel is the world's longest train tunnel. (Photo by Arnd Wiegmann/Reuters)

Huellas, a paraplegic dog in a wheelchair, walks at Pescadores beach in Chorrillos, Lima, September 7, 2015. Sara Moran has an animal shelter called Milagros Perrunos where she cares for stray dogs and shelters dogs injured from traffic accidents or domestic abuses. With donations and raffle, Moran purchases wheelchairs, food and medical treatment for the dogs at her shelter. (Photo by Mariana Bazo/Reuters)

Palestinian girl Manar Al-Shinbari (R), 15, who lost her both legs by what medics said was Israeli shelling at a UN-run school where she was taking refuge during the 50-day war last summer, is helped by her sister to put on her headscarf in an apartment in Jabaliya refugee camp in the northern Gaza Strip January 13, 2015. Manar's mother and three of her brothers were killed in the same incident. The girl's family house was destroyed by Israeli shelling during the war. (Photo by Mohammed Salem/Reuters)

Mercedes Formula One driver Lewis Hamilton of Britain sprays champagne at a grid girl as he celebrates his victory on the podium after the Chinese F1 Grand Prix at the Shanghai International Circuit, April 12, 2015. (Photo by Carlos Barria/Reuters)

A couple chats at a park during sunset in Chihuahua November 15, 2014. (Photo by Jose Luis Gonzalez/Reuters)

People take part in a Halloween street party at Lan Kwai Fong on October 31, 2016 in Hong Kong. Halloween, a contraction of All Hallows' Evening, falls on the day before All Saints' Day on November 1, a holiday when Christians remember their deceased loved ones. (Photo by Lam Yik Fei/Getty Images)

A man presents a self-made robot that local media reported is able to carry a person, in Heihe, Heilongjiang province, China, April 5, 2017. (Photo by Reuters/China Daily)

The love padlocks, called cadenas d’amour, multiplied until there were thousands of love tokens on the bridge, each engraved with a message of love. (Photo by Charles Platiau/Reuters)