阅读短文，选择正确的答案。

What do you think the future will be like? Here are some answers from some students.

Mary: If we don't take good care of the Earth now, our children and grandchildren will be born into a world with much pollution. There will be fewer trees and more buildings, because there will be more people.

Linda: I think the life in the futwtn1iaroll.ust people in the world will use "green cars" by 2120, so there will be less pollution and people will live to be 200years old. As for (至于)space travel, I would say, we will visit Mars in about fifty years.