keep back
留下
例句1, The teacher asked the students to keep back their questions until the end of the lecture.
老师要求学生们把问题留到讲座结束再问。
例句2, She decided to keep back some of her savings for emergencies.
她决定留一部分储蓄以备不时之需。
例句3, The police had to keep back the crowd to ensure the safety of the event.
警察不得不拦住人群以确保活动的安全。

keep doing sth.
继续做某事
例句1, Despite the challenges, she decided to keep doing her best in every task.
尽管面临挑战，她决定继续在每项任务中尽力而为。
例句2, He told himself to keep doing his exercises daily to stay healthy.
他告诉自己要坚持每天锻炼以保持健康。
例句3, The teacher encouraged the students to keep doing their homework regularly.
老师鼓励学生们继续定期完成作业。
例句4, Even when tired, they decided to keep doing the project until it was finished.
即使很累，他们还是决定继续做这个项目直到完成。
例句5, She promised to keep doing her part to help the community.
她承诺继续为社区尽自己的一份力。

keep off
勿踏; 勿踩
例句1, Please keep off the grass to maintain its beauty and health.
请勿践踏草坪，以保持其美丽和健康。
例句2, The sign clearly says “Keep Off” to prevent accidents.
标志上明确写着“勿踏”，以防止事故发生。
例句3, She decided to keep off sugary drinks to improve her health.
她决定不喝含糖饮料以改善健康。
例句4, The teacher warned the students to keep off the topic during the debate.
老师警告学生在辩论中不要涉及这个话题。

keep on
继续（进行）
例句1, We need to keep on practicing if we want to win the competition.
如果我们想赢得比赛，就需要继续练习。
例句2, Despite the difficulties, she decided to keep on pursuing her dreams.
尽管有困难，她还是决定继续追求她的梦想。
例句3, The teacher told the students to keep on working until the bell rings.
老师告诉学生们继续工作，直到铃声响起。
例句4, He keeps on forgetting to bring his homework to school.
他总是忘记把作业带到学校。

keep one’s word
守信
例句1, He always keeps his word, so I trust him completely.
他总是守信，所以我完全信任他。
例句2, She promised to help me with the project and she kept her word.
她承诺帮我完成这个项目，并且她信守了诺言。
例句3, Keeping your word is essential in building strong relationships.
守信是建立牢固关系的关键。
例句4, Despite the challenges, he managed to keep his word and deliver on time.
尽管面临挑战，他还是信守诺言并按时完成了任务。

keep up
保持; 维持; 继续
例句1, It’s important to keep up with the latest trends in technology to stay competitive in the job market.
保持与最新技术趋势同步对于在就业市场中保持竞争力至关重要。
例句2, She struggled to keep up with the fast pace of the marathon, but her determination kept her going.
她在马拉松比赛中努力跟上快节奏，但她的决心让她继续前进。
例句3, The teacher encouraged the students to keep up their good work and not to give up on their studies.
老师鼓励学生们继续保持良好的学习状态，不要放弃学业。
例句4, He tried to keep up a cheerful demeanor despite the challenges he was facing.
尽管面临挑战，他仍努力保持乐观的态度。

knock at
敲
例句1, She gave a gentle knock on the door before entering.
她轻轻地敲了敲门，然后进去了。
例句2, The sudden knock at the window startled everyone in the room.
窗外的突然敲击声让房间里的每个人都吓了一跳。
例句3, He received a knock on his confidence after the failed presentation.
在演讲失败后，他的自信心受到了打击。
例句4, The boxer delivered a powerful knock to his opponent, ending the match.
拳击手给了对手一记重击，结束了比赛。

knock into sb.
撞上
例句1, She didn’t see the door and accidentally knocked into it.
她没看到门，不小心撞上了。
例句2, He was in a hurry and knocked into a stranger on the street.
他匆忙赶路，在街上撞上了一个陌生人。
例句3, The car knocked into the tree due to the slippery road.
由于路面湿滑，汽车撞上了树。