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.

用所给动词的正确形式填空。