?Keep (all) your wits about you (idiom) -
To pay attention and be ready to react.（保持清醒，随时应变）
1. Cycling is potentially very dangerous in the city - you have to keep your wits about you.
2. Luckily, my father kept his wits about him and saved us from the fire.
?Not bear thinking about (idiom) -
To be too shocking or unpleasant to think about.（难以想像）
1."What if she'd been driving faster?""It doesn't bear thinking about."
2.What had happened to her before dying did not bear thinking about.
?The crux (noun) -
The most important or serious part of a matter, problem, or argument.（关键，要害）
1.The crux of the country's economic problems is its foreign debt.
2.The crux of the trial was his whereabouts at the time of the murder.
?Rack one's brain(s) (idiom) -
to strain in mental effort, esp to remember something or to find the solution to a problem.（绞尽脑汁，搜肠刮肚）
1. I've been racking my brain all day but I can't remember her name.
2. He racked his brains all weekend trying to think of a solution to the problem.
?Above all else (idiom) -
Used to emphasise that a particular thing is more important than other things.（高於一切）
1. Above all else I hate the cold.
2. Many people value money above all else.