用所给动词的适当形式填空。

1. — I _____ (buy)a beautiful pen.

    — When _____ you ____  (buy) it?

2. He _____ (not post) the letter for me. It is still on his desk.

3. While the Reads _____ (have) supper,the bell rang.

4. He _____ (fall) off the bike last week, so he _____ (feel) terrible.

5. He _____ (ride) his bike this time yesterday.

6. He _____ (look for) his lost brother these years.

7. — What have you done with the apples?

    — We have just _____ (eat) them.

8. Our teacher said that air _____ (keep) moving all the time.

9. — Who _____ (knock) at the door?

    — It's me.

10. Look! The snow _____ (stop). Let's go and make a snowman.