"Once upon a time"是故事的开头常用的英语表达。它来源于古英语中的"an"和"on"，表示"曾经"或"从前"的意思。
例句：
Once upon a time, there was a young prince who pved in a beautiful castle. (曾经有一位年轻的王子住在一座美丽的城堡里)
Once upon a time, in a land far, far away, there was a magical kingdom. (曾经，在一个遥远的地方，有一个神奇的王国)
Once upon a time, there was a poor boy who pved with his mother in a small cottage. (曾经，有一个又穷又小的男孩和他的母亲住在一间小屋里)