如图，在正方体ABCD﹣A₁B₁C₁D₁中，P为BD₁的中点，则△PAC在该正方体各个面上的射影可能是____．

观察下列等式：

① $\sqrt{1\text{-}\frac{1}{2}}\text{=}\frac{1}{2}$ ；② $\sqrt{2\text{-}\frac{2}{5}}\text{=}2\sqrt{\frac{2}{5}}$ ；③ $\sqrt{3\text{-}\frac{3}{10}}\text{=}3\sqrt{\frac{3}{10}}$ ；④ $\sqrt{4\text{-}\frac{4}{17}}\text{=}4\sqrt{\frac{4}{17}}$ ；……

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.

了解和正确选择、使用地图，可以方便我们的生活．有关下列四幅地图的叙述，错误的是（    ）