Paramedics carry an injured woman out from a subway station after a rush-hour subway train derailment, to be transported by a medical helicopter in Moscow, Russia, on Tuesday, July 15, 2014. A rush-hour subway train derailed in Moscow Tuesday, killing 20 people and injuring at least 150, emergency officials said. Several cars left the track in the tunnel after a power surge triggered an alarm, which caused the train to stop abruptly. (Photo by Ivan Sekretarev/AP Photo)

A feeder trains a Siberian tiger cub at Erdaohe Tiger Park July 2, 2006 in Antu County of Yanbian Chaoxian Autonomous Prefecture, Jilin Province, China. About 15 artificially-fed Siberian tigers from Harbin Siberian Tiger Park are being trained to develop their ability to live in the wild. The wild Siberian tiger is listed as one of the most endangered species in the world, with its existing number estimated at around 400 worldwide, mainly in the northeastern part of China and the Far East of Russia. Reportedly there are more than 1,300 Siberian tigers which have been raised in China. (Photo by China Photos/Getty Images)

Young girls practice acrobatic skills in the Sichuan Provincial Art School July 14, 2008 in Chengdu of Sichuan Province, China. (Photo by China Photos/Getty Images)

School boys who attend Sri Lankan traditional dance training wait for their graduation ceremony at a Buddhist temple in Colombo, Sri Lanka January 23, 2017. (Photo by Dinuka Liyanawatte/Reuters)

A Palestinian female volunteers for the al- Aqsa Martyrs Brigade, a militant group part of Fatah movement, stands with her weapon in this undated photo. Unlike Hamas and Islamic Jihad, the ideology of al-Aqsa is rooted in Palestinian nationalism not political Islam, and is the only Palestinian group that accepts and trains women to be “martyrs”. (Photograph by Courtney Kealy/Getty Images)

In this photo taken Wednesday, November 26, 2014 attack dogs and their handlers apprehend a “rhino poacher” center, after alighting from a helicopter into water, in a simulation exercise showing training at an academy run by the Paramount Group, near Rustenburg, South Africa. The course prepares canine units to find firearms or contraband, track suspects in the undergrowth and abseil in harnesses from helicopters in pursuit of poachers. Dogs and handlers learn to trust each other and fine tune a relationship balancing control and aggression. (Photo by Denis Farrell/AP Photo)

Traditional Hungarian horsemen pose as one of them cracks his whip over his horse in the Great Hungarian Plain in Hortobagy, Hungary June 30, 2016. (Photo by Laszlo Balogh/Reuters)

Bosnian worker Sefik Salihovic drives a steam engine in the Bosnian town of Banovici, 140 kms (86.9 miles) north of Sarajevo, on Monday, November 24, 2014. Every day, steam engines over 60 years old, defy their age and still pull wagons of coal from Banovici's coal mine to clients in nearby towns. But in the summer some of them turn into the only tourist attraction this impoverished north Bosnian town has to offer. (Photo by Amel Emric/AP Photo)