1 就像这个句子：I saw him two weeks ago == It is two weeks SINCE i saw himsince後面的saw是瞬间动词== I haven't seen him for two weeks (这里的not seen成了延续动词)2 He got to Shanghai two days ago (got...他抽烟五年了==it is five years since he BEGAN to smoke. 他戒烟五年了===it's five years since he smoked.