3．knock off撞掉下来

　　 A child ran into the street and knocked the woman off her bicycle．

2．knock down撞倒

　 They make sure the cows not knock the young trees down or eat the leaves．．

1．knock at敲(门、窗等)

　 Yon should knock at the door before coming in．

11．keep off使……远离

　 Please keep off the grass．

10．keep／prevent／stop．．．from doing sth．制止(防止)……做某事

　 The heavy rain kept us from going out．

9．keep silent保持沉默

　 He kept silent．about the matter．

8．keep in touch with与……保持联系

　 We have kept in touch with each other by writing letters．

7．keep one’s word遵守诺言

　 I am sure you will keep your word．

6．keep out of使……不进入

　 In the ancient time, the Great Wall was built in order to keep enemy out of country．

5．keep away from远离

　 Keep children away from fire．