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)

A visitor tries a baccarat game at the Global Gaming Expo (G2E) Asia in Macau, China May 19, 2015. (Photo by Bobby Yip/Reuters)

A couple who did not give their names walk in downtown Havana, February 2, 2015. (Photo by Alexandre Meneghini/Reuters)

Ma Jiaqi, 5, and her mother arrive at Beijing Railway Station for their train to Changchun of Jilin province, in Beijing, China, January 25, 2016. According to traffic police, over 2.9 billion trips will be made around China during the 40-day Spring Festival travel rush, which started on January 24. (Photo by Jason Lee/Reuters)

Float builder Andrea works on a float which depicts Russia's President Vladimir Putin as warmonger, at the float hall of the Mainz Carnival Association (MCV), in Mainz, Germany, 02 February 2016. The MCV invited journalists to a preview of this year's floats for the upcoming Shrove Monday carnival parade. The main carnival season festivities will happen around Rose Monday on 08 February. (Photo by Fredrik von Erichsen/EPA)

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)

DJ David Guetta (R) and rapper Nicki Minaj perform onstage during the 2017 Billboard Music Awards at T-Mobile Arena on May 21, 2017 in Las Vegas, Nevada. (Photo by Mario Anzuoni/Reuters)

Miniscule larvae carve winding tunnels as they eat through small leaves in a small forest near the town of Velbert in western Germany in July 2022. The hungry green sawfly larvae measure just three millimetres in length and are difficult to spot on the leaves of the beech tree unless up close. (Photo by Christian Brockes/Solent News)