选择适当的句子，完成对话

A. It makes the air dirty. B. We should ride a bike more often. C. The air is clean and fresh there. D. It's from factories, cars and buses. E. I'm going to the Huangshan Mountain.

Lily: Where are you going this winter holiday?

Mike：

Lily: That's a good idea.

Mike: Yes. Look at the smoke in the sky. Where is the smoke from?

Lily:

Mike：We need to do something to keep the air clean. What should we do?

Lily:

Mike：That's right.