before
单词辨析：
指从现在起往前推算一段时间，通常和一般过去时的动词连用。
He left a moment ago.
他刚走。
There was a pond here three years ago.
3年前，这里有一个池塘。
指过去某时间之前的时间或泛指以前，通常与动词的现在完成时连用，有时也可与动词的过去完成时或一般过去时连用，也可用于具体的一段时间；在间接引语中用 before 而不用 ago。
Have you heard about it before?
你过去听说过这件事吗？
I have never met him before.
我以前从未见过他。
He said that he had met the man somewhere before.
他说他以前在什么地方见过这个人。
He was in Italy the week before.
他前一个星期在意大利。
泛指以前，有时常用于对比。
Formerly, Ted often lingered around a park, with nothing to do.
从前，特德时常在公园里闲逛，无所事事。
He was formerly a worker, but now he is a manager of a shop.
他曾经是个工人，可现在他是一家商店的经理。
与 before 用法相同，但更加正式。
I haven't met him previously.
我以前没有见过他。
She previously worked as a teacher.
她过去当过教师。
Six months previously he had quitted his job.
6个月前他辞职了。
相关例句：
The turn is about two kilometres before the roundabout.
拐弯就在环岛前面约2公里处。
It was some time before the door opened in response to his ring.
他按完门铃后过了一会儿门才打开。
We will train you first before we set you a task
我们在给你分派任务之前会先对你进行培训。
Before leaving, he went into his office to fill in the daily time sheet.
离开前，他到自己的办公室填写了日常考勤表。
I saw before me an idyllic life.
展现在我眼前的是充满诗情画意的生活。
We waited three months before going back to see the specialist.
我们等了3个月才回去见那位专家。