In this photo taken Tuesday, October 14, 2014, skulls and bones are stacked at the Catacombs in Paris, France. The subterranean tunnels, stretching 2 kilometers (1.24 miles), cradle the bones of some 6 million Parisians from centuries past and once gave refuge to smugglers. The site used to close at 5 p.m., but is now staying open until 8 p.m. The change is mainly aimed at allowing more people to visit and reducing long lines, since it can only hold a limited number of people at a time and visits can't be reserved in advance. (Photo by Francois Mori/AP Photo)

“Car2go fleet is located throughout the greater downtown area and can be accessed on-demand or booked 24 hours in advance. The members may use the vehicle for as long as they like, without committing to a specific return time or return location”. – Wikipedia

Photo: A car2go employee shows how members can use a smartphone or iPad app to locate and reservec car2go vehicles March 22, 2012 in Washington, DC. Beginning March 24, car2go will offer the first free-floating car-sharing service in Washington and Portland, Oregon, where customers can use the smartphone app within the 34-square-mile “Home Area”. After paying a one-time $35 membership fee, drivers can then rent the Smart Fortwo vehicles by the minute, paying only for the time they use the vehicle, with discounted rates for hourly and daily use. (Photo by Chip Somodevilla/Getty Images)

Thor, Virginia Tech College of Engineering, Robotics and Mechanisms Laboratory, tries to connect the hose to a firehose connection during the hose task at the Homestead-Miami Speedway, Friday, December 20, 2013, in Homestead, Fla. (Photo by Alan Diaz/AP Photo)

“The Boeing X-45 unmanned combat air vehicle is a concept demonstrator for a next generation of completely autonomous military aircraft, developed by Boeing's Phantom Works. Manufactured by Boeing Integrated Defense Systems, the X-45 was a part of DARPA's J-UCAS project”. – Wikipedia

Photo: Two X-45A Unmanned Combat Air Vehicles (UCAV) are shown to members of the news media July 11, 2002 at Edwards Air Force Base, California. The X-45A, developed by The Defense Advanced Research Projects Agency and the Boeing Company, is the first unmanned system designed from inception for combat missions. (Photo by David McNew/Getty Images)

Houthi followers perform the traditional Baraa dance ahead of a demonstration against the Saudi-led air strikes in Yemen's capital Sanaa August 24, 2015. The nothern-based Houthis, a Shi'ite Muslim group, took control of Sanaa last September. Arab countries intervened in the conflict in March to halt a Houthi advance into the south which caused the Saudi-backed government to flee to Riyadh from its refuge in the southern port of Aden. (Photo by Khaled Abdullah/Reuters)

A girl holds her brother in her arm as black smoke rises after an oil well set on fire in the center of al-Kayyara town to the south of Daesh terror organization-held Mosul in Iraq on October 25, 2016. The oil well in the center of al-Kayyara town, which was set alight by retreating Daesh militants in advance of the Iraqi army's takeover of the town on August 24, 2016 has still not entirely been put out. The raw petrol which is still alight is creating black clouds above the city. The residents and wildlife beneath this polluting smoke cloud may find their health at risk. The effects of the fire in the town center on unprotected civilians' health can easily be seen on the hands and faces of children playing on the street. (Photo by dris Okuducu/Anadolu Agency/Getty Images)

Camp dwellers pump water from a well at Malkohi refugee camp in Jimeta, Adamawa State, Nigeria on February 19, 2019, four days ahead of the country's General elections set for February 23 after a last-minute rescheduling. Malkohi is a camp for internal displaced who fled their homes as Boko Haram insurgents advanced across north-eastern Nigeria. From their homes on the outskirts of Yola, capital of presidential candidate Atiku Abubakar's home state Adamawa, Malkohi residents say they feel forgotten. (Photo by Luis Tato/AFP Photo)

Syrian girls carry bags with bread as people queue up outisde a bakery in a rebel held neighbourhood in the northern city of Aleppo on July 12, 2016. Since mid-2012, Aleppo has been roughly divided between government control in the west and rebel control in the east, and has suffered enormous destruction in the war that has killed more than 280,000 people nationwide. Last week, a government advance brought regime troops within firing range of the Castello Road, the only remaining supply route into the opposition-held east, effectively severing rebel neighbourhoods from the outside world. With their route to the outside world cut, there is no new flour coming to the city's bakeries, and fuel to light their ovens is also now hard to find. (Photo by Karam Al-Masri/AFP Photo)