Members of Japan's idol group “Virtual Currency Girls” wearing cryptocurrency-themed masks perform in their debut stage in Tokyo, Japan, January 12, 2018. Japanese female idols have teamed up to form the ‘Virtual Currency Girls’ group to promote the knowledge of cryptocurrencies through entertainment. Each of its 8 members represents a cryptocurrency: bitcoin cash, bitcoin, ether, neo, nem, ripple, mona, and cardano. (Photo by Kim Kyung-Hoon/Reuters)

A supporter of the team of Ukraine cheers prior to the Euro 2016 Group C soccer match between Ukraine and Poland at the Velodrome stadium in Marseille, France, Tuesday, June 21, 2016. (Photo by Thanassis Stavrakis/AP Photo)

Tank crew standing in front of M-4 tank, Ft. Knox, Kentucky, June, 1942. (Alfred Palmer/OWI/LOC)

In this photograph taken on August 25, 2016, an Afghan shepherd watches over his sheep as they graze on the outskirts of Herat. (Photo by Aref Karimi/AFP Photo)

A girl sits on railway tracks at a makeshift camp for refugees and migrants at the Greek-Macedonian border near the village of Idomeni, Greece, March 19, 2016. (Photo by Alkis Konstantinidis/Reuters)

Mrs. Marie Graskamp of Milwaukee shows the different positions one might assume when entering the bomb shelter in Milwaukee September 3, 1958. This circular entrance is about three feet in diameter. This is the entrance (according to the builders) that would connect to the cellar of a home assuming the shelter was in the ground for added protection. If a bombing should occur, all members of family would proceed to the cellar and then through the circular port into the shelter. (Photo by AP Photo)

Evel Knievel is shown in his rocket before his failed attempt at a highly promoted 3/4-mile leap across Snake River Canyon in Twin Falls, Idaho, on September 8, 1974. The jump failed when the parachute on his rocket malfunctioned, opening prematurely. Knievel was uninjured. (Photo by AP Photo)

Londoners sleep on the platform and on the train tracks at Aldwych Underground station,London, during heavy all night Nazi bombing raids, October 8, 1940. (Photo by AP Photo)