A police officer stands at a police cordon near the scene of a terror attack in London, U.K., on Sunday, June 4, 2017. A van swerved into Saturday-night crowds on London Bridge, before three men got out and went on a stabbing rampage through nearby bars. (Photo by Luke MacGregor/Bloomberg)

Iraqi children play with a ball on a street blocked with burning tyres, amid a general strike in the southern city of Basra, on November 25, 2019. The demonstrations rocking the capital and Shiite-majority south since October 1 are the biggest grassroots movement the country has seen in decades. Sparked by outrage over rampant government corruption, poor services and lack of jobs, they have since gone straight to the source: calling out the ruling system as inherently flawed and in need of a total overhaul. (Photo by Hussein Faleh/AFP Photo)

American students going wild during their Spring Break week-long recess in Cancun, Mexico on March 10, 2007. (Photo by Keystone USA/ZUMA Press/Rex Features/Shutterstock)

National Guardsmen are put through riot training in Boston's Commonwealth Armory on Friday, October 18, 1974. Massachusetts Gov. Francis W. Sargent called up the guard to quell school violence, but the city has been relatively calm and the guard has remained in the armories. (Photo by JWG/AP Photo)

Finding just the right spot above the clouds at Camp 1 on Ama Dablam, Danuru Sherpa uses his iPhone to catch up with friends and family. Even at 18,500 feet (5,654 meters), climbers here can check their email and other dispatches from the world below. (Photo by Aaron Huey/National Geographic)

A man presents a self-made robot that local media reported is able to carry a person, in Heihe, Heilongjiang province, China, April 5, 2017. (Photo by Reuters/China Daily)

People stand in front of a black ribbon, symbolising remembrance and mourning, being projected onto the Sydney Opera House on February 9, 2023 in solidarity with Turkey and Syria after a massive earthquake devastated the two countries. (Photo by David Gray/AFP Photo)

(L-R) Jesse Montana , Kyle Chan, James Kennedy and Anthony F. attend Kyle Chan's “Star Wars vs. s*xy Aliens” Birthday Party at Sofitel Hotel on February 19, 2019 in Los Angeles, California. (Photo by Robin L Marshall/Getty Images)