happen是不及物動詞。happen用法主要有以下三種：
1. "sth.+happen+地點/時間"，意為"某地/某時發生了某事"。
例如：An accident happened in that street.那條街發生了一起事故。
What"s happening outside?外面發生什麼事了？
2. "sth.+happen to+sb."意為"某人出了某事(常指不好的事發生在某人身上)"。
例如：A car accident happened to him yesterday.昨天他發生了交通事故。
What happened to you?(=What was wrong / the matter with you?)你怎麼啦？
3. "sb.+happen+to do sth."意為"某人碰巧做某事"。
例如：I happened to meet her in the street.我碰巧在街上遇見她。
It happened that I was out when he called.他來訪時我碰巧不在。
happen是不及物動詞。happen用法主要有以下三種：
1. "sth.+happen+地點/時間"，意為"某地/某時發生了某事"。
例如：An accident happened in that street.那條街發生了一起事故。
What"s happening outside?外面發生什麼事了？
2. "sth.+happen to+sb."意為"某人出了某事(常指不好的事發生在某人身上)"。
例如：A car accident happened to him yesterday.昨天他發生了交通事故。
What happened to you?(=What was wrong / the matter with you?)你怎麼啦？
3. "sb.+happen+to do sth."意為"某人碰巧做某事"。
例如：I happened to meet her in the street.我碰巧在街上遇見她。
It happened that I was out when he called.他來訪時我碰巧不在。