In the future, because of high technology(科技), there will be a time machine. With the time machine, people can go to both the past and the future. But most people would like to go to the past and don't like to go to the future, because the environment(环境)in the future will be very bad. There will be few trees and animals. And there will be a lot of rubbish(垃圾).

Not everyone can go to the past or the future. You have to be more than 18 years old, Before your travelling, you need to fill in a form (填写一张表格). You need to write your name, age and the reason to take the journey. When you go there, you can't take anything with you. And you have to come back in three days. When you comeback, you can't bring anything back.