once

This quiet street was once a bustling market during the Roman Empire.

(Chinese) 这条安静的街道在罗马帝国时期曾是一个繁华的市场。

The actor, once a household name, is now rarely recognized in public.

(Chinese) 这位演员，曾经家喻户晓，现在在公共场合很少被认出来。

I only need to remind you once to finish your homework before dinner.

(Chinese) 我只需要提醒你一次，在晚饭前完成作业。

The Hale-Bopp comet, visible to the naked eye in 1997, orbits the sun only once every 2,533 years.

(Chinese) 海尔-波普彗星在1997年肉眼可见，每2533年才绕太阳运行一次。