since和before的区别!It is thirty years since we last met.这句话用before怎么说?since和before的区别到底是什么?这种It is句型什么是用since?什么时候用before?

since和before的区别!It is thirty years since we last met.这句话用before怎么说?since和before的区别到底是什么?这种It is句型什么是用since?什么时候用before? ----It's a long time ( ) I saw you last.----Yes,and what a pity it is now that it will be a long time ( ) we see each other again.A before since B since when C since before D when before 考察的知识点是什么,since和before,when的区别when是 it is + 一段时间 +since 和 it is + 一段时间 + before的区别 it is + 一段时间 +since 和 it is + 一段时间 + before的区别 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 before和since的用法及区别如题. since和before的用法有什么区别呢 It be .when It be .before It be .since的区别 long before和long since 区别 it is some time before与it is some time since 的区别是什么,请举例说明, it's + a period of time + before/since 的区别?it's + a period of time + before... 与 “it's + a period of time since...”的区别是什么?什么时候用 since 什么时候用 before I had ever seen it before.和[I had never seen it before.]有什么区别? since,after,when before的区别 since、 before、 ago 他们的区别是什么 英语单选（关于since和before)How long do you suppose it is ＿＿ he arrived there?A.before B.since 两者有什么区别? it was years before i had seen her 和it wasyears since i had seen her是相等吗 since 和before 作“以前”解释时的用法和区别? 英语中since和before的用法?