用所给动词的正确形式填空。

1. Did you see the accident ______ this morning? (happen)

2. You should get a chair ______on. (sit)

3. There are so many children ______ (play) in the park on Sundays.

4. It's hot. You'd better ______ both the windows and the doors. (open)

5. It's not easy ______ fish with your hands only.(catch)

6. Our teacher asked us to ______ page 16. (turn)

7. You must ______ to the teacher carefully in class. (listen)

8. He felt ______ (worry) about his son at that time.

9. He found a number of people already ______ (work) in the workplace.

10. Many children trust animals because they know ______ (keep) a secret.