keep doing sth 和keep on doing sth 有什么区别

keep doing sth.坚持做某事
强调状语的继续,常与表示延续动作的动词与静止状态的动词连用,如(hope,think,wonder,dream,sit,stand,lie,sleep等)
He kept talking until the meeting was over.他一直在说,直到会议结束.
He kept eating/ smiling/ walking.他一直在吃/笑/走.
She keep running她一直在跑（没停过）
He kept standing in the street .他一直站在大街上.
Please keep sitting where you are.
We’ll keep going forward.
We kept hoping that they would chance to come to china (again) some day.
keep on doing sth.表示动作反复,强调动作与动作之间有间隔,常与表示短暂动作的动词连用.“坚持做某事”,克服困难继续坚持.
He kept on ringing me up,but I don't want to keep in touch with him any more.
他不断地给我打电话,可我不想和他保持联系了.
The boy kept watching the passing traffic at the gate.
这个男孩在门口不停地看着过往的车辆.
She kept on raising her hand她反复举手（不是一直举着手）
He kept on repeating these words over and over.他一遍又一遍重复这几句话.