1.ago adv. 以前
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。
She gave up teaching three years ago.
三年前，她放弃了教学工作。
There was a pond here three years ago.
3年前，这里有一个池塘。
She was hired three years ago.
她是三年前录用的。
We went there a couple of years ago.
我们几年前去过那里。
She died ten years ago but her memory lives on.
她十年前就去世了，但她却留在人们的记忆中。
Just a few years ago the picture was very different.
几年前的情况就大不相同。
Her parents died a long time ago.
她的父母很早以前就去世了。
South America separated from Africa 200 million years ago.
2亿年前南美洲和非洲分离。
The house was pulled down long ago.
那栋房子很久以前就被拆掉了。
She joined the company three months ago.
她三个月前进了这家公司。
2.before adv. 先前，以前
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。
She's lived there since before the war.
她从战前起就一直住在那里。
Leave your keys at reception before departure.
离开前请把钥匙留在服务台。
Do it before you forget.
尽早动手，免得忘了。
He had died a month before.
他一个月之前就死了。
Have you heard about it before?
你过去听说过这件事吗？
Annie was born a few weeks before Christmas.
安妮出生在圣诞节前几周。
I have never met him before.
我以前从未见过他。
He spent his early life in Sri Lanka before moving to England.
在移居英格兰之前，他早年是在斯里兰卡度过的。
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。
Did she leave a message before she went?
她走之前留言了吗？
He took a cold shower and then towelled off before he put on fresh clothes.
他冲了个凉水澡，用毛巾擦干身子后换上了新衣服。
Kelman had a book published in the US more than a decade before a British publisher would touch him.
克尔曼早在英国出版商同他接触前十多年就已经在美国出版过一本书了。
Stock prices climbed close to the peak they'd registered before the stock market crashed.
股价几乎攀升到了股市崩盘前的历史最高位。
He spent his early life in Sri Lanka before moving to England.
在移居英格兰之前，他早年是在斯里兰卡度过的。
There was additional work to be done before all the troops would be ready.
在全军准备就绪之前，还有一些杂事必须处理。
Before Gallacher could catch up with the ball, Nadlovu had beaten him to it.
加拉赫还没来得及追上球，纳德洛武就已经抢先一步触到球了。
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。
3.formerly adv. 以前，从前
泛指以前，有时常用于对比。同义词：previously
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。
Formerly he often lingered about [ around] a park, doing nothing.
从前他时常在公园里逛荡，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。
I learnt that the house had formerly been an inn.
我得知这座房子以前是家客栈。
John Marsh, formerly of London Road, Leicester, now living in France
约翰∙马什，以前家在莱斯特市伦敦路，现居住在法国。
He had formerly been in the Navy.
他从前在海军服役。
This area was formerly within the sphere of influence of the US.
这一地区先前属于美国的势力范围。
What was formerly a sandbank has now become fertile paddy fields.
原来的沙滩如今变成了米粮川。
The formerly [ once] barren land has been changed into stretches of fertile fields.
昔日的荒地今天成了良田。
4. previously adv. 以前，先前
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。
She had rented the flat from the council some fourteen months previously.
大约14个月以前，她从地方政府那里租下了这套公寓。
He had first entered the House 12 years previously.
12年前，他首次成为议员。
Guyana's railways were previously owned by private companies.
圭亚那的铁路以前是归私有企业所有的。
I should like to add a corrective to what I have written previously.
我想对我先前写的内容进行补充修改。
The building had previously been used as a hotel.
这座楼房早先曾用作旅馆。
The contract was awarded to a previously unknown company
合同签给了一个之前并不知名的公司。
The document was previously circulated in New York at the United Nations
这份文件先前在纽约的联合国总部传阅过。
Previously she had very little time to work in her own garden.
以前，她没什么时间打理自己的花园。
Some drugs are being used on a much larger scale than previously.
与以前相比，某些药物的使用范围更广了。
He may suddenly take a dislike to foods that he's previously enjoyed.
对以前爱吃的食物，他兴许突然就没了胃口。
Spassky had never previously lost to his antagonist.
斯帕斯基以往从未输给过他的对手。
The two fighters had previously boxed a 12-round match.
这两位拳击手之前已经打了一场12回合的比赛。
She previously worked as a teacher.
她过去当过教师。
I haven't met him previously.
我以前没有见过他。
Previously our mountain area [ region] is poor and impoverised.
先前咱们山区很穷。