There are some 250 milion cars in America, 250 milion cars in the country with just over 300 milion people. And most of those vehicles, of course, are gas(答案：powered）. This poses a huge challenge given the limited supplies of oil and the growing(答案：urgency）of the global warming crisis. But there is good news, according to our guests today. And that is we have the know-how and the technology to build(答案：sleek) , fast automobiles that don't use gasoline. These vehicles of tomorrow are powered by(答案：hydrogen) , electricity, bio-fuels, and digital technology. And they already exist. So what's stopping us from putting them on the roads? Our guests today will help answer that.
