A Hawaiian cleaner wrasse provides its cleaning services to a yellowfin goatfish in a reef community off the Big Island in Hawaii. Cleaner species help rid their hosts of ectoparasites, dead tissue, bacteria and fungi. Studies have shown cleaning to play a vital role in keeping many reef ecosystems healthy. (Photo by Marty Snyderman/Caters News Agency)

Thousands of heavy-duty trucks loaded with coal are lined up for up to 130 kilometres from the Mongolia-China border on a sole road in the Gobi desert, Mongolia, October 29, 2017. The journey can take more than a week. (Photo by Bazarsukh Rentsendorj/Reuters)

Bicycles of various bike-sharing services are seen at an urban village in smog during a polluted day in Shanghai, 2017. Rapid expansion of shared bicycle companies across China has led to massive piles of abandoned bikes as supply outstrips demand. (Photo by Aly Song/Reuters)

Concertgoers dance at the Coachella Valley Music and Arts Festival in Indio, California, U.S., April 15, 2018. Coachella became one of the world' s premier music festivals not only for the A- list performers. The two- weekend party in the California desert has become a major event in its own right for the fashion. While designers have heavily marketed their brands to Coachella, the fans who draw the most notice often do so by embracing their own sartorial flair, driven by a sense of innovation and, among revelers in the searing heat, of inhibition. (Photo by Mario Anzuoni/Reuters)

Girls in swimsuits participate in the Grelka Fest at the ski resort Sheregesh in Tashtagolsky District of Kemerovo Oblast, Russia on April 15, 2018. Skiers and snowboarders from around the world marked the end of the 2017-18 winter season. Wearing bikinis and bathing shorts a total of 1,525 claimed a new Russian record for the daring downhill escapade – in a temperature of around 5ºC. In fact, more have taken part in this GrelkaFest event in the past, but not during an official record attempt. (Photo by Kemerovo Online/The Siberian Times)

A passenger (L) gets inside a decorated matatu as other passengers wait for it to fill at night in the streets of Nairobi, Kenya, 24 March 2018. The Matatu culture is very big in Kenya, the minibuses are decorated with colorful graffiti inside and outside and most of them are equipped with TV screens, high-speed internet, and power sockets. (Photo by Daniel Irungu/EPA/EFE)

Students from the University of St Andrews jump into The North Sea, as a good luck tradition before exams start on the East Sands in St Andrews, Fife, Scotland on May 1, 2018. (Photo by Derek Allan/Alamy Live News)

American model and television personality Kendall Jenner attends the Tiffany & Co. Paper Flowers event and Believe In Dreams campaign launch on May 3, 2018 in New York City. (Photo by Jamie McCarthy/Getty Images for Tiffany & Co.)