Complete the following sentences adding a principal or a subordinate clause with a suitable form of the verb. 1. It was some time since ……. 2. They were still waiting when ……. 3. …… after the teacher left (had left). 4. We hadn't been there for ten minutes before ……. 5. The doctor had scarcely examined the patient when ……. 6. …… since he returned from his expedition. 7. …… since we have been talking. Let's go home. 8. …… while we were discussing the matter. 9. …… as he sat thinking it over again and again. 10. …… when the train arrived. 11. He will answer your letter after ……. 12. …… till the lesson is over. 13. …… before you ask such silly questions. 14. …… as long as you can. 15. …… as soon as he comes to Moscow. 16. …… before he (had) told her the news. 17. …… until the car passed. 18. …… when the plane had already taken off.