A pro-Russian rebel guards a captured former Ukrainian Army checkpoint outside Vuhlehirsk, Donetsk region, eastern Ukraine, Thursday, February 5, 2015. The rebels have closed in around the town in a strategy they triumphantly refer to as the Debaltseve cauldron. Separatists recently burst through government lines in the rural settlement of Vuhlehirsk. (Photo by Vadim Braydov/AP Photo)

Indonesian motorists push their motorbikes as they wade through a flooded street outside the presidential palace in Jakarta, Indonesia, 09 February 2015. Incessant rain overnight triggered widespread flooding in the Indonesian capital Jakarta, bringing traffic to a standstill. The city hall in central Jakarta and the front lawn of the presidential palace were inundated in up to 20 centimetres of water, television pictures showed, after heavy rain. (Photo by Mast Irham/EPA)

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)

In this Wednesday, March 18, 2015 photo, limestone quarry workers walk through a cloud of dust spewed into the air by rotor blades of the stone-cutting machinery in the desert of Minya, southern Egypt. Around 45,000 people, including children, work in an estimated 1,500 quarries, digging out stones that later will be used in construction or powdered to be used by pharmaceutical and ceramic companies. (Photo by Mosa'ab Elshamy/AP Photo)

Revellers wearing lanterns parade through the streets during the carnival procession of Basel, Switzerland, 15 February 2016. The traditional Morgestraich starting Monday morning after Ash Wednesday at 4 a.m. marks the kick-off of the Carnival of Basel. (Photo by Patrick Seeger/EPA)

Refugees and migrants try to find a place on an already full train headed for Serbia, near the city of Gevgelija, The Former Yugoslav Republic of Macedonia, on February 24, 2016. Refugees and migrants from Iraq and Syria continue to pass through Macedonia on their way to the European Union. (Photo by Georgi Licovski/EPA)

A musher handler with Alan Eischens team embraces one of Eischen's dogs just before the ceremonial start of the Iditarod Trail Sled Dog Race that begins a near 1,000-mile (1,600-km) journey through Alaska’s frigid wilderness in downtown Anchorage, Alaska March 5, 2016. (Photo by Nathaniel Wilder/Reuters)

A tractor trailer drives through flash flood waters that overran Skunk Creek, Tuesday, August 19, 2014, in northwestern Phoenix. Flooding from heavy rain in the Phoenix area has forced authorities to close several major roads, including a portion of Interstate 17 about 25 miles north of the city. (Photo by Matt York/AP Photo)