1 . Imagine sitting inside a windowless train that's shooting through a tube at twice the speed of an airplane. Your train has no wheels, produces no _________ , makes its own electricity, and isn't affected by bad weather. This is the hyperloop, a new vision for the world's _________ , safest, and greenest form of transportation. Many have _________ this new technology, but others say the hyperloop vision is just a bunch of hot air.

Hyperloop developers plan to use the properties of magnets to float, stabilize, and drive the capsules or pods for hundreds of miles through _________ tubes. Without air or ground to slow down the vehicles, what was once a five-hour journey would become a half-hour excursion, engineers promise.

Supporters of the technology promote additional _________ of transporting passengers and cargo by hyperloop. For example, they firmly state that unlike other city-to-city transport that's _________ , such as planes or trains, hyperloop vehicles would leave as needed, like Ubers and taxis. While the _________ would hold only 28 to 50 passengers each, developers plan for them to depart stations in groups every minute or so which they say could amount to shuttling 50,000 people an hour. That's more than twice the passenger _________ of the world's fastest trains.

Developers also say that hyperloop tubes would be _________ so they wouldn't interfere with other traffic or threaten wildlife. And tubes would be covered with solar panels to power the hyperloop's systems. ____________ , advocates regard the hyperloop as the transportation choice for the future.

But not everyone is on board. Engineers have calculated that the high-speed vehicles will need to make much wider turns than currently envisioned, and otherwise they won't be ____________ for passengers. This would add several miles to the proposed tube tracks, Engineers also say planners haven't included enough time for vehicles to safely brake and take off at stations. Some engineers believe it will take much longer than claimed to pump the ____________ out of the tubes before each vehicle's departure. Critics thus say hyperloops can't go as fast or serve as many passengers per hour as advertised, making them ____________ existing high-speed transportation options.

Hyperloop companies say they're ____________ these concerns. They claim that they can safely maintain high speeds by having the vehicles bank around the turns as a plane does. And their hyperloops will rely on the split-second reaction times of a computer to ____________ vehicles quickly, frequently, and safely.