补全对话

A. Do you know what the world's population today is? B. I'm reading a book about the world's population. C. What's the population? D. It's too terrible. E. It was no more than 250 million. F. I think we must do something to control the population. G. There are too many people on the earth.

A: What are you doing?

B:

A: Can you tell me something about the book?

B: Certainly! It says about 1, 000 years ago, the world's population was very small.

A: Really?

B: Yes, but during the last three or four hundred years, the world's population has grown very quickly.

A: Sorry, I don't know.

B: It's more than 7 billion.

A: It's so large.

B: Yes. If we don't control the population, there will not be enough space to live in.

A: