过去式： knew

过去分词： known

第三人称单数： knows

现在分词： knowing

I don't know what to make of the new manager.

这位新经理，我不知道怎么评价他才好。

These problems are all in your mind, you know.

你知道，这些问题都只是你的凭空想象而已。

You'll like her once you get to know her.

你一旦了解了她就会喜欢她的。