It is ...+ since ...与It has ...+since ...的区别?It has been 2 years since we began to learn English．It is thirteen years since Hong Kong returned to China.今天在一本书上看到这两个句子,语法上都是对的吗?如何区别?

It is five years since he smoked it is ...since ..为什么不用完成时it is 100 years since Qinghua university was found. it is ...since it was...before 一定是过去式吗? 为啥it is some time since与it has been some time since没区别 it is some time since+...与it has been some time since+...什么区别? 什么时候用It was+一段时间 +since,什么时候用It is +一段时间+since? It is +一段时间+since+从句 和 beforeIt is +一段时间+since(before)+从句 since 和before 有什么区别吗 since it anyway,it is still my home,because It is my life.翻译成中文 It is years since we meet last time.（纠错） It is +一段时间+ since【用的是什么时态?】 It is three years since she was in the It is/has been + since sb + 具体,简洁. It is ten years since he ____(join) the army It is+时间段+since+时间点.可以说一个例句吗？ It is/has been+since sb+did 怎么用? 改错：It is 3 weeks since Ihave seen him. It is a week since he has been to BeiJing. it is 3 years since Tom has been abroad