Pedestrians cover their face as they walk along the dusty road in Kathmandu, Nepal February 27, 2017. Nepal has forced 2,500 old vehicles off roads in its capital city of Kathmandu, part of a fight against alarming air pollution levels that have hit nine times World Health Organisation (WHO) limits. Air pollution has been a chronic problem in rapidly growing Kathmandu, which sits in a Himalayan valley and is home to more than 3mn people. (Photo by Navesh Chitrakar/Reuters)

Blacksmith Johann Schmidberger works on a suit of armour for the Vatican's Swiss Guards at his workshop in Molln, Austria, March 29, 2017. Austrian blacksmiths who produce ceremonial suits of armour for the Vatican's Swiss Guards are close to the end of their current deal to do so, and say supplying the suits will not now be an issue for many years to come. One of the drawbacks of the Swiss Guards' medieval uniforms is that the craftsmanship needed to make them is disappearing. (Photo by Leonhard Foeger/Reuters)

A model wears a floral headdress at the Royal Horticultural Society's Chelsea Flower show in London, Britain, May 22, 2017. The prestigious Chelsea Flower Show, held annually since 1913 in the Royal Hospital Chelsea grounds, is open to the public from the 23rd to the 27th of May, 2017. (Photo by Dylan Martinez/Reuters)

Bison along the Bitterroot Valley's Eastside Highway north of Stevensville, Montana, are covered in snow following a blizzard on November 23, 2010. (Photo by Perry Backus/The Missoulian)

A workman smooths out the gravel near the base of British artist Alex Chinneck' latest sculpture “A bullet from a shooting star” on the Greenwich Peninsula in London on September 17, 2015. The 35-metre tall, upside-down electricity pylon overlooks the Canary Wharf financial district. (Photo by Leon Neal/AFP Photo)

A dune buggy driver trains before competing in a sand dune drag racing event on January 8, 2016, as part of the Liwa 2016 Moreeb Dune Festival in the Liwa desert, some 250 kilometres southwest of Abu Dhabi. The festival, which attracts participants from around the Gulf region, includes a variety of races (cars, bikes, falcons, camels and horses) or other activities aimed at promoting the country's folklore. (Photo by Karim Sahib/AFP Photo)

Members of Chinese Shaolin Temple Warrior Monks perform martial arts during the “Cultures of China, Festival of Spring” Gala in Toronto, Canada, on February 27, 2016. (Photo by Zou Zheng/Xinhua/Sipa USA)

In this October 5, 2016 photo a man looks at the work “Not to be Reproduced” by Rene Magritte at the Kunsthalle art gallery in Hamburg, Germany. The exhibition, which runs from Oct. 7, 2016 until Jan. 22, 2017, features more than 150 masterpieces of surrealism from four of the most significant European private collections of the 20th century. (Photo by Daniel Reinhardt/DPA via AP Photo)