Bài tập 1: Cho hình thức đúng của đông từ trong ngoặc.
1. I’ll come and see you before I ……........... (leave) for the States.
2. John …….............. (read) a book when I saw him.
3. Almost everyone ……................. (leave) for home by the time we arrived.
4. Henry ……................ (go) into the restaurant when the writer was having dinner.
5. He will take the dog out for a walk as soon as he …….............. (finish) dinner.
6. Before you asked, I …….................... (write) these letters
7. He fell down when he ……................ (run) towards the church.
8. The light went out while I........................... (have) dinner.
9. They .................... (help) her as soon as they have completed the work.
10. You will see him when he............................... (come) here tomorrow.