Once I finish this project, I will take a vacation.（一旦我完成这个项目，我就会去度假。）

She once lived in Paris for a year.（她曾经在巴黎住过一年。）

Once you understand the rule, it's very easy.（一旦你理解了规则，就非常简单了。）

He once told me a very interesting story.（他曾经给我讲过一个非常有趣的故事。）

Once the rain stops, we can go outside.（一旦雨停了，我们就可以出去。）

They once went on a road trip across the country.（他们曾经进行过一次横穿这个国家的公路旅行。）

Once in a while, I like to treat myself to a nice dinner.（偶尔，我喜欢好好吃一顿晚餐犒劳自己。）

Once upon a time, there was a beautiful princess.（从前，有一位美丽的公主。）

Once you make a promise, you should keep it.（一旦你许下诺言，就应该遵守它。）

I once tried skydiving, and it was an amazing experience.（我曾经试过跳伞，那是一次奇妙的经历。）

Once the sun sets, the temperature will drop.（一旦太阳落山，温度就会下降。）

My father once worked in a factory when he was young.（我父亲年轻时曾在一家工厂工作。）

Once you start learning a new language, don't give up easily.（一旦你开始学习一门新语言，不要轻易放弃。）

She once participated in a singing competition and won first prize.（她曾经参加过一场歌唱比赛并获得一等奖。）

Once the movie starts, please be quiet.（电影一开始，请保持安静。）

We once had a big party to celebrate our victory.（我们曾经举办过一个盛大的派对来庆祝我们的胜利。）

Once he gets home, he usually reads books for a while.（他一到家，通常会读一会儿书。）

Once the snow melts, spring will be here.（一旦雪融化，春天就来了。）

They once helped an old lady carry her groceries.（他们曾经帮助一位老太太提她的杂货。）

Once you see the sign, turn left.（一旦你看到那个标志，就向左转。）