Boys play basketball in the facilities of Belarus' Republican Clinic of Speleotherapy within a salt mine, as part of their treatment, near the town of Soligorsk, south of Minsk, February 19, 2015. According to the state clinic, more than 7,000 children and adults seek medical treatment for respiratory illness each year in the subsurface chambers of its facilities, located 420 metres underground between layers of potassium and stone salts in an operational salt mine. (Photo by Vasily Fedosenko/Reuters)

A boy carries sugar cane through a farm on the outskirt of Zaria in Nigeria's northern state of Kaduna November 15, 2016. (Photo by Akintunde Akinleye/Reuters)

A Ukrainian serviceman fires a 2S7 Pion self-propelled gun during military exercises near the village of Divychky in Kiev region, Ukraine, October 21, 2016. (Photo by Valentyn Ogirenko/Reuters)

Only 156 people remained in the tribe when Jan visited in Accham District, Nepal, January 2016. Hidden deep in the Himalayan forest is one of the world’s last enduring nomadic tribes who are resisting attempts to move them into permanent settlements. (Photo by Jan Moller Hansen/Barcroft Images)

The six-months-old female koala cub holds on to the back of zoo keeper Lena at the zoo in Duisburg, Germany, 23 October 2015. The yet unnamed baby weighs 580 grams. (Photo by Roland Weihrauch/EPA)

A visitor looks at a creation by Russian artist Irina Nakhova presented at the Russia's pavilion during the 56th International Art Exhibition (Biennale d'Arte) titled “All the Worlds Futures” on May 5, 2015 in Venice. (Photo by Gabriel Bouys/AFP Photo)

Nepalese women farmers spray mud water at each other while planting rice in a paddy field during the National Paddy Day in the village of Jitpur in Kathmandu, Nepal, 30 June 2015. On this day, known as Asar Pandra, farmers begin the annual rice planting season and mark the day with various festivities such as preparing rice meals with muddy water, spreads mud among farmers. The Mud being a symbol for a prosperous season. The agricultural sector contributes about 60 per cent to Nepal's gross domestic product. (Photo by Narendra Shrestha/EPA)

A protester holding a torch runs past police (not pictured) trying to stop the protesters from marching in a rally organised by a 30-party alliance led by a hardline faction of former Maoist rebels, who are protesting against the draft of the new constitution, in Kathmandu August 15, 2015. The group says that the draft is not inclusive and does not protect the rights of the marginalised and underprivileged groups in the country. (Photo by Navesh Chitrakar/Reuters)