根据下面的对话情景，在每个空白处填上一个适当的句子，使对话的意思连贯、完整。

A: Hi, Mark! Have you ever been to Beijing?

B: Yes, I have.

A:

B: I went there to visit my pen friend last month.

A:

B: He has been there since he went to Beijing University.

A:

B: Yes, we have. We visited the longest wall there.

A: I've never been there. But this summer I will go there with my parents.

B: Great!

A: Thank you!