Talking about the twenty first century, I think there will be huge changes in the way people use cars. Laws will be made about what kind of car you can own, and when you can use it.
Maybe there'll just be too many of them on the roads. The air will be so seriously polluted that nobody will be able to breathe normally.
Exactly, people will have to rely on trains.
Why do you say that?
Well, we won't be able to use cars and the airports take too much space. That leaves trains.
Huh? So do you think there'll be more efficient train systems between cities?
Sure, they'll enable people to travel between cities in a matter of hours. There may even be trains going under oceans to connect the main continents.
Under the oceans? Get out of there, I get nervous enough flying on a plane.