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.