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。
Some people don't know when they're well off.
有些人身在福中不知福。
Children can be difficult as we know only too well.
小孩子往往很难对付，对此我们都非常清楚。
There were a whole lot of people I didn't know.
有许多人我都不认识。