it is ...since ..为什么不用完成时it is 100 years since Qinghua university was found.

it is ...since ..为什么不用完成时it is 100 years since Qinghua university was found. it is over a year since i met him 为什么要用since since前不是要用完成时吗? It is five years since we began learning English既然有since为什么要用it is? it is years since i saw him（追加）it is years since i saw him为什么不说it is years since i has seen him而it was years since i had seen him 却可以 since的用法 it+is+一段时间+since+从句为什么这里is可以换成has been但不能换成was it is five years since we began learing English 为什么不是it was 英语翻译It is 3 years since they got marriedIt is 3 years since they married求翻译.为什么都是since可意思完全不一样诶 It is 3 years since he joined the army.为什么用is不用has been it is four years since I joined the army.这里的is,为什么不用was呢? 为什么It is two months since she left Beijing用is不用has been it is since为什么不用完成时就是it is 一段时间+since+过从,为什么be动词是现在时.不是完成时? A:Is your grandpa still smoking B:No,it's years since he smoked.这里为什么用since It is 3 years since he joined the army 和It has been 3 hours since he left his office.为什么一个用is 一个用had been It is 3 years since he joined the army 和It has been 3 hours since he left his office.为什么一个用is一个用has been It is almost five years____we saw each other last time.为什么填since .而不是before it is two years since I started learning English这个句子对吗?为什么? It is three years since I lived here.怎么翻译?为什么这样翻译? It is five years since my father___?后面是用has been dead还是died?为什么?