happen的用法：happen作为不及物动词，基本意思是“发生”、“碰巧”、“遇到”、“恰好”、“出现”、“偶然出现”，指偶然的事故,也可指有计划或无计划发生的事。

happen作为不及物动词，意为（尤指偶然）发生，出现;（作为结果）出现，发生;碰巧，恰好;<主美>碰巧来（或去），偶然出现。

例句：He gave me a guarantee that it would never happen again.

他向我保证这种事情绝不会再发生。

Who can say what will happen next year?

谁能说得出明年会发生什么事？

All these changes happened over a period of time.

所有这些变化都是在一段时间内发生的。

You must on no condition tell them what happened.

你决不能告诉他们所发生的事。

She gave us her version of what had happened that day.

她从她的角度向我们描述了那天发生的事情。

She gave us her version of what had happened that day.

她向我们描述了她认为那天发生的事情。

I give you my word that this won't happen again.

我向你保证这种事不会再次发生。

It happened late last century ─ in 1895 to be exact.

那事发生在上个世纪末——确切地说，发生在1895年。

She brought him up to date with what had happened.

她让他知道最新的情况。

The children gave a confused account of what had happened.

孩子们把发生的事叙述得颠三倒四。

No one knows for sure what happened.

谁也不知道究竟发生了什么事。

Tell me what happened in your own words.

用你自己的话告诉我出了什么事。

Unless something unexpected happens, I'll see you tomorrow.

如果不出意外，我明天去看你。