Young U.S. visitors pose for a photograph next to a vintage car in Havana March 16, 2016. (Photo by Ueslei Marcelino/Reuters)

A Chinese man uses an old film camera to take a picture of relatives near the Forbidden City on March 27, 2014 in Beijing, China. (Photo by Kevin Frayer/Getty Images)

A picture made available on 09 September 2015 shows traditional mud men dancers from the Asaro District of Goroka in the Eastern Highlands Province of Papua New Guinea perform for the official opening of the Pacific Islands Forum in Port Moresby, Papua New Guinea, 08 September 2015. The Pacific Islands Forum goes from 07 to 11 September and discusses the regions vulnerability to Climate Change. (Photo by Mick Tsikas/EPA)

Tourists pose with pigeons in the flooded St. Mark's Square in Venice, on November 7, 2014. The high water, a combination of high tides and a strong Scirocco wind in the Adriatic Sea, stood at 110 centimeters early on November 7. The city has for years been wrestling with the problems posed by the threat of rising sea levels. (Photo by Olivier Morin/AFP Photo)

This artist's scoreboard displays a fictional game between Mars and Earth, with Mars in the lead. It refers to the success rate of sending missions to Mars, both as orbiters and landers. Of the previous 39 missions targeted for Mars from around the world, 15 have been successes and 24 failures. For baseball fans, that's a batting average of .385. The United States has had 13 successes out of 18 attempts, or a “batting average” of .722. NASA's Curiosity rover, set to land on the Red Planet the evening of Aug. 5, 2012 PDT (morning of Aug. 6 EDT), will mark the United States' 19th attempt to tackle the challenge of Mars, and the world's 40th attempt. (Image by NASA/JPL-Caltech)

Chinese women run with a ball on a snow covered field in Shenyang in China's northeastern Liaoning province during International Women's Day on March 8, 2018. International Women's Day is celebrated on March 8 every year and commemorates the movement for women's rights. (Photo by AFP Photo/Stringer)

An exile Tibetan monk gestures as he makes a point in a dialectics debate with another monk, sitting right, at the Kirti monastery in Dharmsala, India, Monday, January 18, 2016. The debate is an essential part of their training as Buddhist monks. (Photo by Ashwini Bhatia/AP Photo)

Labourers pour molten iron into a container at a foundry in Xiangfan, Hubei province in this July 2, 2010 file photo. Iron ore is enjoying its biggest rally in years, outpacing copper and oil so far in 2016, but still weak forward prices show it may be tough to stretch the bullish outlook. Improving steel prices in top market China are helping fuel iron ore's climb as producers gear up for a seasonal uptick in demand. Yet there is no shortage of doubters who see gains in the bulk commodity as fleeting given a large glut and challenges for China's economy. (Photo by Reuters/Stringer)