持续性动词
持续性动词， 用来表示主语继续或保持一种状况或态度的动词。
持续性动词表示持续的行为或状态，常见的有
be, clean, do, drink, drive, eat, fly, have, keep, know, learn, lie, live, play, rain, read, run, sing, sit, sleep, speak, smoke, snow, stand, stay, study, talk, wait, walk, wear, work, write
持续性动词可用于现在完成时态，并可与表示一段时间的状语连用。一段时间的状语如:
for three years, since last month, how long, during the past two months 等。如:
I know her very well because we have been friends for over ten years.
我很了解她，因为我们已是十年的老友。
I have learned English since I came here. 自从我来到这儿就学英语了。
持续性动词不能与表示短暂的时间状语(点时间)连用。如: It rained at six yesterday morning. 这句话语法上是有错的。因为 at six 表示“点时间”，而rain 是持续性动词。
如果要用持续性动词表示一时短暂的动作，可以在其前加上come to, begin to, start to, get to等。
It started to rain at six yesterday morning. 昨天上午6点开始下雨。
When did you get to know him? 你什么时候认识他的。
