2、表示“某人出了某事(常指不好的事)”,要用“sth.+ happen+to sb.”这一结构来表达.例如：a car accident happened to her this morning.今天上午她发生了交通事故。
3、表示“某人碰巧做某事”,要用“sb.+ happen+ to do sth.”这一结构来表达.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个朋友。
4、happen表示“碰巧或恰巧发生某事”时,还可用“it happens / happened that...”这一结构来表达.例如：it happened that brian and peter were at home that day.碰巧那天布莱恩和彼得在家了。