选内容补全对话。                                 

A. How big is it? B. Is it very old? C. I'm reading a book about Beijing. D. How long is it? E. Can you go with me?

Amy: Hello, Sam. What are you doing?

Sam: That's very interesting.

Amy: Oh, tell me more about Beijing. 

Sam: It's got about twenty million people.

Amy: Wow! That's very big.

Sam: Yes, it is. And there's a famous Great Wall in Beijing.

Amy: Really? 

Sam: It's more than twenty thousand kilometres long.

Amy: Wow! It's really long. I want to visit it some day.

Sam: Yes, I'd love to.