three years has passed____ he knew this 是before还是when

Tom has( )for three years Three years has past.为什么“three years”可以看做单数? pass是延续性动词吗pass动词表示经过的时候是延续性动词还是瞬间性动词?如：Three years has passed.中的pass是瞬间动词还是短暂动词? Three years ___(pass)since I left school.急! his mother died .she has been_____for three years Mr Green has been in Beijing since three years ago. Tom has-- for three years Agone Bbeen away Cleft Dcome Mr Wang has taught _(they) English for three years he has lived in village for three years.同义句 JIM has studied in Australia for three years. The old man has been dead for three years The old man has been dead since three years ago.区别 Three years has passed since he came to China.中为什么用has不是说three years吗 three years His grandfather died three years ago.(用for three years 改写句子)那么我写成His grandfather has died for three years .错在哪里?为什么 Eight years (has|have) pass since he left选什么 讲下理由啊 It is three years since he died.(同义句） He has ____ _____ for three years. My brother has joined the army for three years.(同义句改写)My brother has____ ____ solider for three years. Mr wang has been an english teacher since three years ago.对since three years ago .提问