keep doing、keep on doing的用法和區別:

1. keep doing側重表示"持續不停地做某事"或"持續某種狀態"。
例:The girl kept crying all the time. 那個女孩一直在哭。
The baby kept sleeping about four hours. 這個嬰兒連續睡了大約四個小時。

2. keep on doing 表示"總不斷做某事",不表示「靜止狀態」。不能與sitting, sleeping, lying, standing這類詞連用。

例:It kept on raining for seven days.
Don't keep on asking such silly questions.