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 how _________ (keep) a secret.