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?

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? 英语中since和before的用法? 关于before和sinceit was+一段时间+before还是since?关于这两个词还有什么用法? 单选 it is 30 years ____we last met.句型it is ……since 和it is~before 这两个句型怎么区分 关于since和beforeIt was two years___he came back from abroad.A.since B.that C.when D.before long before和long since 区别 since和before哪个前后时态一致? 一道初三英语单选Scientist say it may be a few years ____ it is possible to test the new medicine on patient A.because B.after C.before D.since 关于初三英语since,和for如何使用? 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 请问英语中since和before具体用法 什么主句过去式、从句什么啦(打个比方) 英语单选和填空 关于since和before的用法.Jerry has been in the school library for two years ______he left school.A.before B when C since D as soon as 英语选择题（when,before,since,after)Nearly two thousand years have passed the Chinese first inventd the compass.A.when B.before C.since D.after主要说说为什么选它和那四个词应该注意的用法,浅层次的我会,但是深层的就 before和since的用法及区别如题. since和before的用法有什么区别呢 关于英语祈使句和间接引语.1.对于直接引语和间接引语中.直接引语是过去时态.像 before ,when while since ,if 条件句 等 他们是如何 变换的.如：he said he finished his homework before he came in 如何变换? 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?