Andrea Petkovic of Germany in action against Sara Errani of Italy during day one of the Mutua Madrid Open tennis tournament at the Caja Magica on May 3, 2014 in Madrid, Spain. (Photo by Julian Finney/Getty Images)

In this Thursday, May 8, 2014 photo, guests look down from the Tilt!, a new tourist attraction that provides guests a unique view of the downtown area from the 94th floor of the John Hancock Building, after it was unveiled in Chicago. People hold onto handrails as the glass and steel facade tilts forward 30 degrees. (Photo by Ashlee Rezin/AP Photo/Sun-Times Media)

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)

A singer drinks from a huge bowl of beer on-stage as he pays tribute to the customers after performing at an entertainment club in Beijing, on May 8, 2014. (Photo by Jason Lee/Reuters)

Promotional models use their smartphones during their break at the Global Mobile Internet Conference in Beijing May 6, 2014. Mobile Internet industry executives, developers and investors from more than 30 countries took part in the Global Mobile Internet Conference in Beijing, the organiser said. (Photo by Kim Kyung-Hoon/Reuters)

A brown bear is checked by foreign veterinaries and local staff members at the Four Paws Bear Sanctuary in Pristina, on May 9, 2014. (Photo by Hazir Reka/Reuters)

A Russian-made rifle, carried by this woman when she was captured in Nearby Brush, is slung around her neck by South Vietnamese soldiers before they began their interrogation of her as Viet Cong suspect near AP La Ghi in Vietnam, August 25, 1965. The girl behind the woman, also was captured in the brush. (Photo by AP Photo)

U.S. Army helicopters providing support for U.S. ground troops fly into a staging area fifty miles northeast of Saigon, Vietnam, August 28, 1966. Helicopter fuel is stored in the large rubber tanks, foreground. (Photo by Henri Huet/AP Photo)