More advanced vocabulary

to keep one’s wits about one	To be ready to think clearly and calmly about something that may be difficult
to be at one’s wits’ end	Very worried because you have tried everything possible to solve a problem
to be scared out of one’s wits	Very frightened
to the best of one’s knowledge	As far as I know
common knowledge	Everybody knows about it
to have something on the brain	Keep thinking about something all the time so that it annoys you
to pick somebody’s brains	Ask someone a lot of questions to find out everything they know about a particular subject to help you
to rack one’s brains	Try very hard to think of an idea or remember something
to set one’s mind on something/doing something	To be determined to achieve something or decide that you definitely want to have it
to spring to mind	To think of somebody or something immediately