happen是一個動詞，一般都是指已經發生了的事情，所以慣用What happened這樣的過去式。如：What happened? You seem nervous.發生什么啦？你似乎很緊張。

happen的用法例句：

1.Remember, keep a positive attitude and good things will happen.

記住：保持樂觀的心態，好事自然會發生。

2.Do not wait for good things to happen to you. You need to walk towards happiness.

不要等待好事降臨，你要向幸福進發。

3.This is such an unforeseeable situation that anything could happen.

這種情況很難預測，什么事都有可能發生。

4.I go all tingly when I think of what might happen.

我一想到可能發生的事就滿心歡喜。

5.He couldn't help worrying obsessively about what would happen.

他禁不住時刻擔心將會發生的事情。

6.When events happen that shake these beliefs, our fear takes control.

當一些事情的發生動搖這些信念時，恐懼就會占據我們的心靈。

7.Lucy shut her eyes so she wouldn't see it happen.

露西閉上了眼睛，這樣就不會看到它發生了。

8.Deep inside the awareness was stirring that something was about to happen.

內心深處隱隱感覺到有什么事即將發生。

9.She wondered what would happen if her parents found her.

她不知道如果父母找到自己會有什么結果。

10.To start with, where and when did it happen?

首先，這事發生在何時何地?