关于现在完成体的瞬时动词与延续性动词间的变换问题。

have started/begun to do sth.-->have done sth意思是开始做某事，当我们遇到前面这个（start、begin）瞬间动词用于一段时间（2 hours）时要变为后面这个句型have done sth，done是延续性动词do（这里的do是做的意思），不能用瞬间动词。当我们遇到for +一段时间 或 since+过去的时间点（since 2 years）就要转换为延续性动词。如：open,stop,like,love,die,win,close,shot,begin,start enter,finish 等为瞬间动词用于时间段时都要做相应的变换的，当然要记忆一下的。希望能帮助你，欢迎追问！

for加一段时间，表延续性
动词可分为短暂性和延续性动词，对于非延续性动词，就要用for加一段时间
I have received his letter for two days.{错的}
I received his letter two days ago.{对的}
I have had his letter for two days.{对}
It is two days since I receive his letter.对