"why is there a moat?"“它是什么朝代修的？“爸爸，“古代人真聰明，”媽媽說，” how can there be a river under the wall?"”爸爸說，a few days ago，護城河，“為什么有護城河？"what dynasty was it built?" 前幾天，"the ancients were very clever." i touched my head and said.”爸爸有些不肯定的說。