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.

下列说法正确的是（  ）

写出该化学反应的符号表达式：____

十五边形的外角和等于____ ${}^{\circ }$ ．