Couples take part in a competition during a mass wedding of 64 doctoral student couples at Harbin Institute of Technology, a university in Harbin, Heilongjiang province, China, June 4, 2017. (Photo by Reuters/Stringer)

An Iranian Shiite Muslim prays in Laylat al-Qadr, or the night of destiny, during holy fasting month of Ramadan after midnight, in central Tehran, Iran, early Sunday, June 18, 2017. Laylat al-Qadr is the night when Muslims believe the Quran was first revealed to prophet Muhammad. Worshipers gather in religious ceremonies to pray, ask forgiveness and make wishes on one of the most important nights of the Islamic calendar. Shiite Muslims, the vast majority of Iranians, believe the night happens either on 19th, 21st or 23rd of the holy month of Ramadan. (Photo by Ebrahim Noroozi/AP Photo)

Breitling Wingwalkers aircrafts perform during an aerobatic display at an air show in Zhengzhou, Henan province, China, September 25, 201. (Photo by Reuters/Stringer)

Russian soldiers from 34th motorized infantry mountain brigade, 58th Army, prepare to evacuate a fellow soldier acting as an injured person during a drill at the Darial range outside Russia's city of Vladikavkaz, July 28, 2010. (Photo by Kazbek Basayev/Reuters)

The Jet Propulsion Lab team's RoboSimian robot turns on a valve at a simulated disaster-response course during day one of the Defense Advanced Research Projects Agency (DARPA) Robotics Challenge finals in Pomona, California, June 5, 2015. (Photo by David McNew/Reuters)

A pistol is lies near the body of a drug suspect who was killed with two others in an alleged “buy-bust” operation before dawn on Friday, September 30, 2016, in Caloocan city, north of Manila, Philippines, in the continuing “War on Drugs” campaign of President Rodrigo Duterte. Duterte said he would be “happy to slaughter” 3 million addicts. (Photo by Bullit Marquez/AP Photo)

A bishop walks past a new street-art collage by Italian artist Maupal showing Pope Francis playing tic-tac-toe and drawing peace signs as a Swiss guard keep watches the street near the Vatican on October 19, 2016 in Rome. (Photo by Tiziana Fabi/AFP Photo)

A boy looks on as fire fighters try to extinguish the fire at oil wells, were set on fire by Daesh terrorists as they fled after Al Qayyarah town's cleansing from Daesh militants as the operation to retake Iraq's Mosul from Daesh continues, in Al Qayyarah Town of Mosul, Nineveh, Iraq on November 02, 2016. (Photo by Yunus Keles/Anadolu Agency/Getty Images)