1. keep doing sth 表示“继续(不断)地做某事”指无停顿或停顿较短。或后接表静态的动词。如：sit sleep. Wait, stand,等。

　　He kept sitting there for half an hour without moving. 他一动不动地在那儿站了半个小时。

2. keep on doing sth 表经过一段时间的间隙后“继续做同一件事”后可接表动态的词。如walk, write talk 等。还暗指不顾困难、反对、警告而“坚持”做某事。

　　They kept on working in the field, though it was raining.虽然天正在下雨，他们还是继续在田里干活。

3. keep sb doing sth. “使某人处于某种状态”

　　Our Chinese teacher kept us reading by ourselves the whole class. 整个一节课， 我们的语文老师都让我们自己看书。

4. keep sb / sth from doing sth. “阻止、防止某人/ 某物做某事”如：

　　① The policeman kept the children from crossing the road when it was dangerous. 危险的时候，这位警察阻止了孩子们过马路。

　　② Be carful! Keep the glass from dropping on to the floor. 当心!防止玻璃掉到地板上。

5. prevent……from doing sth与上同意，但较正式，隐含预防之意。From在被动语态中不可省。如：

　　In many countries, laws have been passed to prevent factories from sending out poisonous gases and polluted water. 许多国家已制定法律来制止工厂排放有毒的气体和污水。

6. stop……from doing sth. 与上可代换。它常指现场的具体行为。如：

　　The policeman stopped the children from playing football in the street. 警察制止孩子们在街上踢球。