A competitor walks on tightrope during a performance in Taizhou, Zhejiang Province, China, May 7, 2016. (Photo by Reuters/China Daily)

Russian Police academy female cadets march during a rehearsal for the Victory Day military parade at Dvortsovaya (Palace) Square in St Petersburg, Russia, Wednesday, May 7, 2014. Victory Day, marking the defeat of Nazi Germany, is Russia's most important secular holiday celebrated on May 9. (Photo by Dmitry Lovetsky/AP Photo)

In this May 24, 2017, photo, DriveTanks.com customers drive on a tank course at Ox Ranch in Uvalde, Texas. The ranch is a free-roaming range filled with exotic animals, some to hunt, and home to DriveTanks.com, where tourists pay to transport themselves into another era and another life. (Photo by Michael Ciaglo/Houston Chronicle via AP Photo)

Stranded cars remain in a flooded street during an intense rainstorm in Havana, on April 29, 2015. Two people were killed, three buildings collapsed and another 24 suffered some kind of damage due to the heavy rain that affected several sectors of Havana Wednesday. (Photo by Yamil Lage/AFP Photo)

A prototype battery-powered plane, called Greased Lightning or GL-10 is pictured flying at NASA's Langley Research Center in this undated handout photo obtained by Reuters May 1, 2015. The plane, which has 10 engines and can take off like a helicopter and fly efficiently like an aircraft, is currently in the design and testing phase. (Photo by Reuters/NASA)

Russian servicemen drive a partially covered T-14 Armata tank along a street before a rehearsal for the Victory Day parade in Moscow, Russia, April 29, 2015. Russia will celebrate the 70th anniversary of the victory over Nazi Germany in World War Two on May 9. (Photo by Maxim Zmeyev/Reuters)

In this photo taken Thursday, May 7, 2015 photo, remains of Soviet soldiers killed during World War II lay in a coffin prior to a reburial ceremony at the Sinyavino Heights memorial near the village of Sinyavino, 50 km (31 miles) east of St. Petersburg, Russia. Hundreds of people came to a World War II battleground outside St. Petersburg this week to bury the remains of 964 Soviet soldiers recovered by volunteer search teams. Fifty crimson coffins containing skulls and bones were solemnly buried at the Sinyavino Heights memorial as Russian war songs played and an honor guard fired a salute. (Photo by Dmitry Lovetsky/AP Photo)

Female Chimpanzee “Fifi” eats carrots as she sits in her enclosure at Taronga Zoo on her 60th birthday May 21, 2007 in Sydney, Australia. Fifi is the oldest of the Zoo's chimp population, which consists of 19 individuals. (Photo by Ian Waldie/Getty Images)