The boy didn't stop singing until their teacher came

Ai giúp mình vs đc ko ạ 
 
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10.The boy didn't stop singing until their teacher came.
>Not until.....
11.She didn't write to him until she received a letter from him.
→It was not until.......
12.The letter wasn't written until yesterday.
...
→Not until.....
13. We didn't have a holiday until last summer.
→It was not until......
14. We couldn't finish it until the end of last summer.
Not until....
15.The child didn't go to sleep until her mother came home.
→It was not until.