清代书法家笪重光所著《书筏》:“将欲顺之,必故逆之;将欲落之,必故起之;将欲转之,必故折之……将欲行之,必故停之。书亦逆数焉。”其书法理论体现了
I'm very proud that Beijing is one of _______ cities in the world.