根据上下文选择句子序号，将对话补充完整。

A. I like summer best. B. He is having a football class. C. Because I can swim in summer. D. I'm reading a book about season. E. Can your brother go swimming with us?

John: What are you doing, Mike?         

Mike:

John: Which season do you like best?

Mike:

John: I like summer, too.

Mike: It's too hot. Let's go swimming, OK?

John: Great!

Mike: No, he can't. He's busy now.

John: What is he doing?

Mike:

John: Oh, next time let's go with him.