It is（has been） two years since I left school这个句子中哪里是主句哪...

it has been three years since i left school（be away for）用括号内 it is two years since I came here还是it has been two years sin It is two years after we left school.这个句子对吗? 为什么It is two months since she left Beijing用is不用has been It _（be) two years since he left school. 初二英语、练习选择It is ten years since Jim left school .ow he has __ 英语翻译It has been two years since I published my first article He said to me,"It is two years since I left shanghai."直接引语转化 请问It is six years since I last met you 与 It has been six yea it has been two day since we left our hometown为什么用has been it has been two days since I started study.这句子对吗? it is 3 years since Tom has been abroad