how为连接副词，引导名词性从句，it后动词可为：一般现在时：动词单数形；一般过去时：动词过去式；还可接情态动词：I don't know how it happened.She will tell you how it can be used.

双语例句

1、Yeah, no, how could he do that?

是啊，不，他怎么可以那样呢?。

2、What? How could you do that?

什么？你怎么可以这样做？

3、How do I know what I should do, what not to do?

我怎么知道我应该做什么，不应该做什么呢？