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)

Japanese chorus girls appear to be drilling in military tactics atop their theater building as they perform salutes, June 30, 1937. The officer is from the Japanese regular army and says the girls display more rhythm in their drills than do the regular troops. (Photo by 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 man watches a wave hit a rock pool at Curl Curl beach as large swell hits the East Coast of Australia on June 6, 2016 in Sydney, Australia. Torrential rain over the weekend saw streets and homes flooded while wind gusts up to 120km per hour brought down trees and powerlines. A king tide has also seen beachside homes evacuated on Sydney's northern beaches as large waves erode the coast. (Photo by Cameron Spencer/Getty Images)

In this picture taken Thursday, August 4, 2016, seal Tristan looks out of a basket while being released into the North Sea together with others at the beach of the island Juist, Germany. He is part of the first group of released seals of the seal breeding station Norddeich this year. (Photo by Carmen Jaspersen/DPA via AP Photo)