I have been somewhere before

曾经───once;去过───been

If you find anything wrong with the machine, you should put it right at once.───发现机器有故障, 要及时排除.

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

Hearing that there was an emergency case, the doctor put down his chopsticks and left at once.───听说有急诊, 医生撂下筷子就走.

She braced herself up and tried once more.───她鼓起勇气又试了一次.

I want to see her once more.───我打算再见她一次.

I met Miquela once, briefly.───我见过蜜凯拉一次，时间很短。

Their attempts at conciliation had failed and both sides were once again in dispute.───他们进行调停的努力失败了,双方再次陷入争吵.

Let's go through the sonata once more.───这个奏鸣曲咱们再练习一遍.

Measure thrice before you cut once.

Once water begins to boil,its temperature no longer rises.

Once bit [bitten] twice shy.

The valiant never tastes of death but once.

He that once deceives is ever suspected.