Aerobatic aircrafts fly during a performance at the Airshow Zhengzhou 2017 in Zhengzhou, capital of central China's Henan Province on April 27, 2017. The 5-day air show kicked off in Zhengzhou on Thursday, aiming to build a general aviation gathering center for business and communications. (Photo by Li An/Xinhua via ZUMA Wire)

Two race pigs jump over an obstacle during a rural festivity in reference to Maria Ascension in San Bernardino, Switzerland on Monday, August 15 2016. (Photo by Samuel Golay/Keystone/TI-Press via AP Photo)

This image obtained January 31, 2017 from the US Geological Survey's Hawaiian Volcano Observatory showing a lava stream, pouring out of the lava tube on the sea cliff at the Kamokuna ocean entry from the Kilauea Volcano on January 29. (Photo by AFP Photo/USGS)

Couples take part in the “Love and Challenge Marathon” in Hanoi, Vietnam, 16 August 2015. Fifty couples, who are going to get married, participated in the event which is held the fifth time. This year, the winners of the marathon received a honeymoon trip to Malaysia. (Photo by Luong Thai Linh/EPA)

People stroll alongside one of the hills of the Tio Pio park in Madrid, Monday, January 25, 2016. The park is a high viewpoint frequented mostly by locals due to its view of the Spanish capital skyline. (Photo by Francisco Seco/AP Photo)

President Calvin Coolidge rides in a car during his inaugural parade in Washington, D.C., U.S. in March 1925. (Photo by Reuters/Library of Congress)

Volunteers carry an idol of the Hindu elephant god Ganesh, the deity of prosperity, in a pond for its immersion during the ten-day-long Ganesh Chaturthi festival in Mumbai, India, September 18, 2015. During the festival, the idols will be taken through the streets in a procession accompanied by dancing and singing, and will be immersed in a river or the sea in accordance with the Hindu faith. (Photo by Shailesh Andrade/Reuters)

Five-month-old baby elephant Fah Jam swims during a hydrotherapy treatment as part of a lengthy rehabilitation process to heal her injured front left foot at a rehabilitation center in Pattaya, Thailand January 5, 2017. The baby elephant was injured at three months old when she got stuck in an animal snare put up by villagers to prevent elephant intrusions in Chanthaburi province. (Photo by Athit Perawongmetha/Reuters)