根据对话内容，在每个空白处填入一个恰当的句子使对话完整、合乎情境。
A: Hello Sandy This is Mary speaking, ____？
B. I'm Xi'an
A. Are you taking a holiday there?
B. Yes. ____？
A: I'm writing a report.
B: ____?
A: It's about the population.
B: Well, I think you can write about the population of Xi' an.
A: Good idea. ____?
B: More than 8 million.
A: Is the population of Xi'an larger than that of Dalian?
B: ____Let me ask my father. Maybe he knows it.
A: All right.
