Yǒu yì tiān, tā zài lùshang yùjian le yí wèi lǎotóngxué.
One day, he ran into an old classmate on the street.
Tips
grammar
Where it stands changes the meaning. Before the verb it means "per day": 一天三顿饭 (three meals a day). After the verb it says how long: 睡了一天 (slept all day).
usage
Set phrases: 一天到晚 (from morning till night), 总有一天 (sooner or later, one day), 一天比一天 (more and more each day).
