体操运动员擦的“镁粉”的主要成分是碳酸镁，其作用是______、______、______．

根据对话内容，从方框内选择恰当的句子将对话补充完整。（选项中有两项是多余的）

A: Hi, Tom! You look very happy today.

B: Oh, yes. Guess what? My best friend Ben is coming.

A: Oh, really? ____小题1:____

B: Tomorrow. I can’t wait to see him.

A: ____小题2:____    

B: For two weeks.

A: ____小题3:____    

B: He is really friendly. I’m sure you will like him when you see him.

A: What does he look like?

B:  ____小题4:____    

A: Could you introduce him to me?

B:  ____小题5:____