If you don't know the answer, just guess. 要是你不知道答案，就猜猜看吧。

How do you know my name? 你怎么知道我的名字？

I knew she wasn't really happy. 我知道她并不是真的幸福。

I don't know where the money's coming from. 我不知道这钱是从哪儿来的。

I need to know if she's made a decision yet. 我需要知道她是否作了决定。

I don't know anything about it. 这件事我一无所知。

We know for a fact that the fire was started deliberately. 我们非常肯定这场火灾是人为的。

We know from experience that unemployment makes the problem worse. 根据经验我们知道失业会使该问题恶化。

I felt I hardly knew my father. 我觉得自己几乎不了解父亲。

She had known Nancy for years. 她已经认识南希很多年了。

They know all their tutors by their first names. 他们直呼所有导师的名字。

We know her mostly for her love poetry. 我们知道她主要是因为她的爱情诗。

I've never known her to make a joke. 我从没见过她开玩笑。