at one's wit's end

例句：

1. 1. She wasso tired that she couldn't continue working after dinner.
   她太累了，晚饭后无法继续工作。
2. 2. He was at his wit's end when he couldn't find a solution to the problem.
   当他找不到解决问题的方法时，他已经到了精疲力竭的地步。
3. 3. The old man was at his wit's end when he realized he had lost his keys.
   当老人意识到他丢失了钥匙时，他已经精疲力尽了。