补全对话

A. I think the number of people living in cities will be larger. B. No problem. C. Where would you like to live? D. When you're free, you can go back to the earth on vacation. E. What will life on the earth be like in 80 years? F. How far is it from Venus to the earth? G. I don't think so.

A: Hey, Jeff!

B: It's hard to say. What's your prediction about that?

A.

B: Oh, no. Then cities will be more and more crowded.

A: In 80 years, some of us will live on another planet.

B: Mars (火星) or Venus (金星)?

A: Mars. I heard scientists found water on Mars.

B: Wow, that's great.

A: You're right.