School teachers and staff members take part during an active shooter training at James I. O'Neill High School in Highland Falls, New York, U.S., December 12, 2017. (Photo by Eduardo Munoz/Reuters)

Brazil's synchronised swimmers Luisa Borges (front) and Maria Eduarda Miccuci perform during a training session at the Rio Olympic Park in Rio de Janeiro, Brazil, April 7, 2016. (Photo by Pilar Olivares/Reuters)

Pakistani passengers ride on crowded train returning from their hometown and villages after celebrating the Eid al-Fitr holiday to mark the end of the Muslim holy fasting month of Ramadan, to Lahore, Pakistan, Monday, July 11, 2016. (Photo by K.M.Chaudary/AP Photo)

A female army recruit attends a base training at the armored battalion in Setermoen, northern Norway on August 11, 2016. Norway has become the first NATO member to have compulsory conscription for women as well as men in the army. Recently, the first batch of army recruits joined the ranks in The Armored Battalion in the Norwegian Army located in Setermoen in northern Norway. (Photo by Kyrre Lien/AFP Photo)

Fire fighters, emergency service vehicles and a helicopter in Moskovsky Prospekt at the entrance to Tekhnologichesky Institut station of the St Petersburg metro in the aftermath of an explosion which occurred in a train at 14:40 Moscow timeon April 3, 2017. (Photo by Peter Kovalev/TASS)

A passenger takes off his pants as others not wearing pants dance while waiting for a subway train during the “No Pants Subway Ride” in Mexico City, Mexico, February 21, 2016. The event is an annual flash mob and occurs in different cities around the world, according to its organisers. (Photo by Carlos Jasso/Reuters)

Jordanian soldiers pose after the opening ceremony of eighth annual Warrior Competition at the King Abdullah Special Operations Training Center (KASOTC) in Amman, Jordan, May 2, 2016. Twenty Seven Teams from Eleven countries are participating in a competition to test their military skills. (Photo by Muhammad Hamed/Reuters)

Migrants scramble aboard a train at the station in Beli Manastir, Croatia September 18, 2015. Migrant numbers in Europe will build up in coming days and their flows may fragment further into new routes, the U.N. refugee agency said on Friday, urging the European Union to grasp a last chance to resolve the refugee crisis next week. (Photo by Laszlo Balogh/Reuters)