Construction work on the tower began in November 2008. Upon its completion this year the building will stand approximately 632 meters (2,073 ft.) high and will have 121 stories. It is expected to open to the public in 2015. (Photo by Rex Features)

Lindsay Heimbach goes airborne while sledding down a hill on Mt. Lemmon December 27, 2008. (Photo by James Gregg/Arizona Daily Star)

An attendee tries Acton's RocketSkates at the 2015 International CES at the Sands Expo and Convention Center on January 6, 2015 in Las Vegas, Nevada. The motorized skates that you strap to your shoes are powered by Lithium Ion batteries and can go up to 12 mph. (Photo by Ethan Miller/Getty Images)

Hungarian Puli sheep dog, Fee, jumps over a hurdle during a preview for a pedigree dog show in Dortmund on Thursday April 24, 2008. (Photo by Frank Augstein/AP Photo)

Steve Jobs, CEO of Apple, attends the Macworld Conference and Expo July 18, 2001 in New York City. (Photo by Mario Tama/Getty Images)

A curious cat ipeeks out of a bag carried by its owner on a tour of the Cat Expo 2022 in Kuala Lumpur, Malaysia, 30 September 2022. The “Ekspo Kucing”, described as Malaysia's Largest Cat Expo runs from 30 September to 02 October 2022 at the Matrade Exhibition and Convention Centre (MECC) in Kuala Lumpur and “will also feature other variety of pets such as rabbits, hamsters, guinea pigs, reptiles and exotic animals”, the MECC said on its website, along with other highlight events such as a Federation Internationale Feline (FIFe) Cat Competition, Cat Adoptions or a “Sugar Glinder Contest”. (Photo by Fazry Ismail/EPA/EFE/Rex Features/Shutterstock)

HRP-4C, a five-foot humanoid robot developed at Japan's National Institute of Advanced Industrial Science and Technology, sings and dances with performers at the Digital Contents Expo in Tokyo on October 17, 2010. The robot runs entertainment software called Choreonoid, a name formed from the words “choreograph” and “humanoid”. (Yoshikazu Tsuno/AFP)

An AH-64D Apache attack helicopter flies in front of a wall of fire during the South Carolina National Guard Air and Ground Expo at McEntire Joint National Guard Base, South Carolina, U.S. on May 6, 2017. (Photo by Jorge Intriago/Reuters/Courtesy Air National Guard)