Soldiers of People's Liberation Army (PLA) Lanzhou Military Region jump through a burning obstacle during a training session at a military base in Tianshui, Gansu province, China, January 6, 2016. (Photo by Reuters/Stringer)

Serena Williams of the U.S. serves during her first round match against Italy's Camila Giorgi at the Australian Open tennis tournament at Melbourne Park, Australia, January 18, 2016. (Photo by Jason O'Brien/Reuters)

UFC women's bantamweight champion Holly Holm and Miesha Tate face off during the UFC 196 weigh ins at the MGM Grand Garden Arena in Las Vegas on Friday, March 4, 2016. (Photo by L.E. Baskow/Las Vegas Sun via AP Photo)

A greater bird of paradise (Paradisaea apoda) displaying in Badigaki Forest, Wokam Island (Aru Islands, Indonesia). Found here in Aru and on adjacent New Guinea, the greater bird of paradise represents about 40 different species of birds of paradise that depend on intact rainforest across the New Guinea region spanning eastern Indonesia and Papua New Guinea. With more than 80% of forest cover still intact, this region represents the largest remaining block of rainforest in the entire Asia-Pacific. (Photo by Tim Laman/naturepl.com/LDY Agency)

World's Greatest Swimming Pools: Four Seasons, Serengeti Pool, Tanzania. A show of elephants, buffalo and baboons awaits thanks to an active watering hole below the free-form infinity pool at this plush hideaway inside Serengeti National Park. Bonus: Because of infrared technology at the hole, guests can be notified on their bedroom TV when animals are approaching. When you've got word of wildlife on the horizon, catch them from your private terrace – or head back to the pool. (From $1,650). (Photo by Four Seasons)

In this Monday, October 8, 2018 photo, Colombia's BMX freestyle athlete Sebastian Martinez practices at the Urban Park, at the Youth Olympic Games in Buenos Aires, Argentina. (Photo by Ian Walton/OIS/IOC via AP Photo)

Kamchatka brown bears at Kurile Lake in Kamchatka peninsula’s volcanic terrain, Russia on August, 2017. Kamchatka brown bears are generally not dangerous to humans, and only 1% of encounters result in attack. (Photo by Igor Ivanko/Anadolu Agency/Getty Images)

An Indian priest worships six-year-old Hindu girl Anushka Chetterjee dressed as the Hindu goddess Durga at a “pandal” for the celebrations of the “Durga Puja” festival in Kolkata on September 28, 2017. The five-day Durga Puja festival, which commemorates the slaying of the demon king Mahishasur by the goddess Durga, marks the triumph of good over evil. (Photo by Dibyangshu Sarkar/AFP Photo)