按照英语语法规则,ago是个后置副词，放在表示时间的词语之后含义指的时间是从现在算起的一段时间之后，只能与一般过去时连用。如：

The letter came a few days ago.

这封信是几天前寄来的。

She was here just a minute ago.

刚才她还在这儿。

He stopped working some time ago.

他早就停止工作了。

He was killed a few days ago in a skiing accident.

几天前他在一场滑雪事故中丧生。

Her parents died a long time ago.

她的父母很早以前就去世了。

Just a few years ago the picture was very different.

几年前的情况就大不相同。

She gave up teaching three years ago.

三年前，她放弃了教学工作。

I used to smoke but I gave up two years ago.

我过去抽烟，但两年前就戒了。

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。

She adheres to teaching methods she learned over 30 years ago.

她依循她30多年前所学的教学法教学。

We went there a couple of years ago.

我们几年前去过那里。

Martha graduated from high school two years ago.

玛莎两年前高中毕业。

South America separated from Africa 200 million years ago.

2亿年前南美洲和非洲分离。

South America and Africa separated 200 million years ago.

南美洲和非洲于2亿年前分离。

The country gained its independence ten years ago.

这个国家十年前赢得了独立。

He stopped working some time ago.

他早就停止工作了。

She was hired three years ago.

她是三年前录用的。

She joined the company three months ago.

她三个月前进了这家公司。

以上都是ago的常见而中规中矩的用法。下两个特殊用法请注意：

1.since+时间段+ago,要用完成时态，如：

He's been there for over two years. He's been there since two years ago.

他在那儿已经待了两年了。自从两年前他已经待在那儿了。

I've kept up a friendship with a girl whom I was at school since twenty years ago.

自从二十年前同学以来我和那个女孩保持着朋友关系。

I have been here since five months ago.

我在这儿已经有五个月了。

I haven't heard from her since ten years ago.

我自从10年前以来就没有收到她的来信了。

I have studied in Peking University since 2 years ago.

我从两年前起，就在北大上学。

2. ag0还可以与情态动态+动词不定式完成时连用,表示现在对过去已发生的事件进行推测或表示现在认为某事本应该发生(含ago的短语并不是修饰情态动词,而是修饰动词不定式完成式的):

He must have left a week ago.他准是在一周前就离开了。

He ought to have been here long ago.他早就应当到这里了。

I seem to have read the book two years ago. 我似乎两年前就读过这本书。

Faber must have seen her a month ago.费伯一个月前一定见过她。

She ought to have been here long ago.她早就应当到这里了。