1. 用方框中所给连词的正确形式填空

before; after; when; while; since; till; until

1. （1） The students didn't go home they finished their homework.
3. （2） Jim has taught English in that school he graduated from the university.
5. （3） I will remain here you can solve the problem.
7. （4） I was writing a letter my mother was chatting with her friends.
9. （5） the boy came in, we were singing an English song.
11. （6） You should read the instruction you use the new machine.
13. （7） the boy watched TV, he went to bed.