根据中文提示，把对话中缺少的内容写在线上。这些句子必须符合英语表达习惯。打句号的地方，用陈述句；打问号的地方，用疑问句。

　　提示：Mary与Bill不期而遇，邀请他一起吃晚饭。但Bill当晚7点要去北京，下周一回来。Mary让Bill回来后给她打电话。

　　(Mary=M; Bill=B)

M: Bill, is that you? I haven’t seen you for a long time.

B: Hi, Mary. Great to see you again.　51　?

M: Fine. Why don’t we get together and have a chat? How about　52　this evening?

B: Well, it sounds great, but I’m 　53　 at 7 o’clock.

M: What a pity!

B: Well, I’ll be back　54　. We can find a time to meet again.

M: Okay.　55　when you are back.

B: No problem. Goodbye!

M: Bye!