如何区分as,while,since,until

在句式中的应用

since prep.自从，自……以来（表示时间，后接名词或从句）
until prep.直到，到……为止
直到……（才），在……前（用于否定句）
as prep. 作为，当作
像…… 如…… 似……
while prep. 直到
conj. 表示“同时”两个动作同时进行

when [(h)wen] conj. 当...时 pron.&ad. 什么时候 例句: the queen's last visit was in may, when she opened the new hospital. 女王上次来访是在五月份，她那时主持了这座医院的落成典礼。 how can they learn anything when they spend all their spare time watching television? 他们把所有的空闲时间都用来看电视了，还能学什麽东西呢？ it was the sort of morning when everything goes wrong. 那天上午就是那样，事事不顺心。 while [(h)wail] conj. 当...的时候 n.&a. 一会儿 v. 消磨 例句: i lived in a hostel while i was a student. 我求学期间住在青年招待所里。 she worked in a bank for a while before studying law. 她学法律之前在银行工作过一段时间。 while mary was writing a letter, the children were playing outside. 玛丽写信时，孩子们在外面玩耍。 since [sins] ad. 后来 conj. 既然,因为 prep. 自从 例句: she moved to london last may and has since got a job on a newspaper. 她去年五月到伦敦，此後一直在报社工作。 it was the first time i'd won since i'd learnt to play chess. 自从我学会下国际象棋以来，这是我第一次赢。 how long is it since we visited your mother? 自从我们看望你母亲以来到现在有多长时间了？ until [ən'til, ʌn'til] prep.&conj. 直到...为止 例句: she was a bank clerk until the war, when she trained as a nurse. 她战前是个银行职员，战时受训当了护士。 he lived in california until he was twenty. 他在加里弗尼亚一直住到20岁. i didn't wake up until i heard the alarm clock. 直到听到闹钟的铃声我才醒来。

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