happen是一个动词，一般都是指已经发生了的事情，所以习惯用What happened这样的过去式。如：What happened? You seem nervous.发生什么啦？你似乎很紧张。
1.Remember, keep a positive attitude and good things will happen.
2.Do not wait for good things to happen to you. You need to walk towards happiness.
3.This is such an unforeseeable situation that anything could happen.
4.I go all tingly when I think of what might happen.
5.He couldn't help worrying obsessively about what would happen.
6.When events happen that shake these beliefs, our fear takes control.
7.Lucy shut her eyes so she wouldn't see it happen.
8.Deep inside the awareness was stirring that something was about to happen.
9.She wondered what would happen if her parents found her.
10.To start with, where and when did it happen?