从所给出的句子中选出合适的选项完成对话。

A. It's about me. B. Let's go swimming, Peter. C. What are you writing? D. Are you doing your homework? E. I'm going to throw it into the sea.

A: Sally is swimming. It's fun.

B: Sorry, Paul. I'm busy.

A:

B: No, I'm not. I'm writing.

A:

B: I'm writing a letter.

A: What is your letter about?

B: I want to put my letter in a bottle.

A: What are you going to do next?

B:

A: Where is it going?

B: I don't know. Maybe it will go to the UK.