请根据对话内容，从方框中选择合适的句子完成对话，每句限用一次，其中有一个为多余选项。

A. I think so. B. Who is he? C. What are you doing? D. I like reading books online. E. I need to write about a great person. F. Then why do you think he is great?

A: Hi, Betty.

B: Hello, Li Ming, I'm searching for information about Nelson Mandela.

A: Nelson Mandela?

B: He was President of South Africa from 1994 to 1999.

A: Err, why are you doing that?

B:

A: I see.

B: He did a lot for the black people in South Africa.

And he won the Nobel Peace Prize(诺贝尔和平奖)in1993.

A: Wow, that's really cool.

B: