They were here an hour ago.一小时前他们在这儿。
He said that his sister had been there three days before.他说他妹妹三天前来过这儿。
<辨析>这两个词都解作“以前”。ago 是副词，表示从现在算起的若干时间以前，谓语动词常用过去时。如：
He can ride a bike now,but he couldn't a few weeks ago.他现在会骑自行车，但几个星期前他不会。
before 也可用作副词，通常表示从过去某时刻算起的若干时间以前，谓语动词常用过去完成时。如：
When we finally got there,the team had left an hour before.我们最后到达那里时，小队已在一小时前离开了。
before 可用在现在完成时、一般过去时的句子里，不伴有具体的时间而单独使用，表示“笼统，不明确的以前”。如：
I have read the book before.我以前读过这本书。
I met that man before.我从前碰见过那个人。
before 还可以用作传记介词或连词，用作介词时，后接某点时间。如：
Please come to see me before six o'clock.请在六点以前来看我。
Where did you sister study before she joined the army?你妹妹参军前在哪里学习？
与单词：ago 相关的例句或者名人名言
These palaces record were copied out three and a half thousand years ago by an egyptian scribe.
这些宫廷的记录是三千五百年前一位埃及的抄写员抄出来的。
From the point of view of evolution, men originated millions of years ago from the anthropoid, a species commonly referred to as the ape man.
从进化的观点来看，人类起源于几百万年前的类人猿，通常又称作猿人。
The warranty lapsed two months ago .
那项保证两个月前失效了。
I came here two days ago.
我是两天前来这儿的。
※Agood horse should be seldom spurred. 好马无需用鞭抽。
※The fiercest agonies have shorest reign.——William Crllen Bryant, American poet最猛烈的痛苦持续的时间也最短。美国诗人 布莱恩特 W C
