happen是不及物動詞,它的用法常見的有如下幾種情況：
1.表示“某地(某時)發(fā)生了什么事”,常用“sth.+ happen +地點/時間”這一結(jié)構(gòu)來表達(dá),此時主語應(yīng)是事情.例如：
The story happened in 2003.這個故事發(fā)生在2003年.
An accident happened in that street.那條街上發(fā)生了一起事故.
2.表示“某人出了某事(常指不好的事)”,要用“sth.+ happen+to sb.”這一結(jié)構(gòu)來表達(dá).例如：
A car accident happened to her this morning.今天上午她發(fā)生了交通事故.
What happened to you?你怎么啦?
3.表示“某人碰巧做某事”,要用“sb.+ happen+ to do sth.”這一結(jié)構(gòu)來表達(dá).例如：
I happened to meet a friend of mine in the street yesterday.昨天我碰巧在街上遇到了我的一個朋友.
4.happen表示“碰巧或恰巧發(fā)生某事”時,還可用“It happens / happened that...”這一結(jié)構(gòu)來表達(dá).例如：
It happened that Brian and Peter were at home that day.碰巧那天布萊恩和彼得在家了.
It happened that he had to take part in a meeting that afternoon.碰巧那天下午他不得不參加一個會議.
注：that從句中的主語是人時,此種結(jié)構(gòu)可以與“sb.+ happen + to do sth.”結(jié)構(gòu)互換.例如：
It happened that Brian and Peter were at home that day.= Brian and Peter happened to be at home that day.