People ride a prototype of a driverless vehicle as it is moves through a pedestrian area in Greenwich, east London, February 11, 2015. Britain has begun testing driverless cars in four cities, launching the first official trials ahead of a series of planned rule reviews to accommodate the new technology. (Photo by Suzanne Plunkett/Reuters)

Tacos of Cochinita Pibil, a popular dish from Yucatan, are seen during an attempt to break the Guinness World Record for the world's longest taco in Guadalajara February 15, 2015. Guadalajara broke the Guinness record for the longest taco of cochinita pibil, with a length of 2.5 kilometers, as part of the COME gastronomy festival, local media reported. For the preparation of the traditional dish, the chefs used 4 tons of pork, 36,000 tortillas and spices for 325 taco servings. (Photo by Alejandro Acosta/Reuters)

Sara Takanashi of Japan, Maja Vtic from Slovenia and Germany's Carina Vogt (R-L) prepare for a training session of the women's Individual normal hill HS100 ski jumping at the Nordic World Ski Championships in Falun February 18, 2015. (Photo by Kai Pfaffenbach/Reuters)

The Aurora Borealis seen across the sky in Lapland, Finland. The beautiful phenomenon was captured by photographer Marko Korosec on a trip to the arctic region of Lapland in Northern Finland. He used long exposures on his Canon DSLR to create the stunning images. (Photo by Marko Korosec/Barcroft Media)

Switzerland's lead Nicole Schwaegli (L) and second Marisa Winkelhausen sweep during their curling round robin game against Japan at the World Women's Curling Championships in Sapporo March 14, 2015. (Photo by Thomas Peter/Reuters)

Urszula Sidoruk, 19, from the paramilitary group SJS Strzelec (Shooters Association), trains her workout at a gym in Siedlce, eastern Poland March 18, 2014. Inspired by the war in Ukraine, growing numbers of Poles are joining volunteer paramilitary groups, where they receive basic army training and prepare to defend their homeland. (Photo by Kacper Pempel/Reuters)

A villager watches as Mount Sinabung volcano erupts, in Kuta Tengah village, Karo Regency in Indonesia's North Sumatra April 1, 2015. The Indonesian volcano was dormant for 400 years before erupting in 2010. (Photo by Y. T. Haryono/Reuters)

People carry cutouts of coffins during a march to commemorate the more than 617 people they say have been killed by law enforcement in LA County since 2000, in Los Angeles, California April 7, 2015. (Photo by Lucy Nicholson/Reuters)