keep on doing 和keep doing 的区别

keep doing / keep on doing
1) 均可表示“继续做某事,反复做某事”,可互换,只是 keep on 更加强调时间的间隔性和动作的反复性,及某人做某事的决心.
He kept on working until midnight though he was tied.
The boy kept /kept on asking some silly questions in class.
2) 若表示一连续不段的动作,或某一动作的持续状态,只宜用keep doing .
She kept waving to her husband until he was out of sight.
They kept standing outside the room during all the meeting.
Keep lying here; I will be back soon.
3) 若表示今后或将来继续做某事,则只宜用keep on doing .
We must keep on working hard in the coming new year.
He kept on smoking though we advised him to stop to smoke.

两者都是“持续做某事”的意思，但是有细微的差别：
keep on doing是指在做着一件事情，中间有段空隙时间（做别的什么事了），然后继续做
keep doing 是指，一直在做某事，没有停止过

be kept dry
保持干燥
The old lady kept on about her illness.
那老太太没完没了地讲她的病情。