【before until since分别前后用于什么时态是否和when的用法相似】

【before until since分别前后用于什么时态是否和when的用法相似】

三个词引导时间状语从句时我区别.before ,until 这两个词用一般现在时表示将来时.如I will wait here until he comes back.It will be two years before he returns.当主句是过去时的时候从句也用过去时.如Yesterday...======以下答案可供参考======供参考答案1:不一样。 before有三种一种是引导状语从句，要满足主将从现，如I'll go home before my mom calls me一种是现在完成时标志，如I have been to China twice before.这时before在句尾一种是过去完成的标志,即before+过去时间点+主句，如, before I came to Jinan,She had already done that. until的用法同before的第一种和第三种，不过翻译不同。 since后加过去时间点或从句，从句要求是一般过去时，且since是现在完成标志，如I have been lived here since 2000或I have been lived here since ten years ago。since可以和for互换，如I have been lived here since ten years ago就等于I have been lived here for ten years.since的翻译是“自....以来”供参考答案2:.时间状语：yet,already,just,never,ever,so far,by now,since+时间点，for+时间段，recently, lately, in the past few years, etc. 现在完成时，基本结构：主语+have/has +p.p（过去分词）+其他时间状语：since+时间点，for+时间段等.现在完成进行时时间状语：Before, by the end of last year (term, month…), etc. 过去完成时，基本结构：主语+had + p.p（过去分词）+其他

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