How often does it play

一次───once;多久───How long?

This area was once a wildlife reserve.───该地区曾是一个野生动物保护区.

I've only been there once.───我只去过那里一次。

She told him to leave the room at once.───她要他马上离开房间.

He determined to go [ that he ( should ) go ] at once.───他决心立刻就 走.

He will explain it fully once and for all.───他将把它充分地解释一次就此了结.

I don't want ifs and buts; swallow your medicine at once.───我可不听你泡蘑菇, 马上吞下你的药.

Once a knave, ever a knave.───一次成无赖, 永远是无赖.

Slavery was once socially sanctioned.───奴隶制曾经为社会所认可.

Once bit [bitten] twice shy.

He that doth most at once doth least.

We hang the walls with wallpaper once a year.

Measure thrice before you cut once.

Once again there's been ferocious blood-letting in the township.