护城河

"why is there a moat?"“它是什么朝代修的？“爸爸，“古代人真聪明，”妈妈说，” how can there be a river under the wall?"”爸爸说，a few days ago，护城河，“为什么有护城河？"what dynasty was it built?" 前几天，"the ancients were very clever." i touched my head and said.”爸爸有些不肯定的说。