it has been three years since i left school（be away for）用括号内

it has been three years since i left school（be away for）用括号内 i have （been away/left） my home for three years.两种我都见过!left为 It has been five years since he has left for beijing这句话对不对啊 It has been 5 years since I was away from the army,but now I Three years ___(pass)since I left school. lucy has been away from hei home for three years It _（be) two years since he left school. he has left since three years ago可以用吗 It has been three hours since he left his office.把has been 换 It has been ten years since I ___(be) a teacher. It has been years since I returned home,为什么since用,而不用when?分不 It has been 4 years since I smoked.怎么翻译?