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When/While/As I was walking down the street,I came across an old friend of mine. 当沿大街行走时,我碰巧遇到了我的一个老朋友。 二、as soon as,immediately,directly,instantly,the moment,the minute,the in- stant,no sooner...than...,hardly/scarcely...when...和once(一……就……) 这些从属连词引导的从句都表示从句的动作一发生,主句的动作随即就 发生,常译为“一……就……”。如: The moment I heard the voice,I knew father was coming. 我一听到那个声音,我就知道父亲来了。 No sooner had we arrived at the station than the train left. 我们一到车站,火车就离站了。 The boy burst into tears immediately he saw his mother. 那个男孩一见到他妈妈便放声大哭。 注意:no sooner...than...;hardly/scarcely...when...这一结构的时态搭配:no sooner与hardly/scarcely引导的句子的谓语动词应用过去完成时,而than与 when引导的句子的谓语动词应用一般过去时。此外,当把no sooner和 hardly/scarcely提到句首时,应用倒装语序。如: I had hardly got home when it began to rain. Hardly had I got home when it began to rain. 我一到家天就下起雨来。 三、till,until和not...until 1.肯定句:主句的谓语动词必须是延续性动词的肯定式,意为“某动作一 直延续到某时间点才停止”。如: He remained there until/till she arrived. 他在那里一直等到她来。 You may stay here until/till the rain stops. 你可以在这里待到雨停。 2.否定句:主句的谓语动词必须是非延续性动词,意为“某动作直到某时 间才开始”。如: He won’t go to bed till/until she returns. 直到她回来他才睡。 3.till不可以置于句首,而until可以。如: Until you told me I had no idea of it. 4.not...until句型中的强调和倒装用法: 直到你告诉我,我才知道这件事。 ①It was not until you told me that I had any idea of it.(强调句型) ②Not until you told me did I have any idea of it.(not until置于句首,主句要 倒装) 四、before和since 1.若表达“还未……就……;不到……就……;……才……;还没来得及… …就……”时,需用连词before。如: We had sailed four days and four nights before we saw land. 我们航行了四天四夜才看到陆地。 We hadn’t run a mile before he felt tired. 我们跑了还不到一英里他就感觉累了。 Before I could get in a word,he had measured me. 我还没来得及插话,他就给我量好了尺寸。 2.before从句中谓语不用否定式。如: Before they reached the station,the train had gone. 他们到火车站前,火车已开走了。 3.It will be+一段时间+before...还要多久才……如: It will be half a year before I come back. 还得再过半年我才能回来。 It won’t be long before we meet again. 过不了多长时间我们就会再见面了。 4.since从句的谓语动词一般是非延续性动词,主句的谓语动词是延续性 的或者是反复发生过的动作。since从句的时态若是一般过去时,相应地, 主句中的时态是现在完成时或现在完成进行时。如: I have written home four times since I came here. 自从我来到这儿,我已经给家里写过四次信了。 She has been working in this factory since she left school. 她离开学校以后就一直在这个工厂工作。 5.在“It is+一段时间+since从句”句型中,时间的计算一律从since从句中 谓语动词所表示的动作完成或表示的状态结束时算起。如: It is three years since the war broke out. 自战争爆发以来有三年了。 It is three years since I smoked a cigar(=since I stopped smoking a cigar). 我不吸烟有三年了。 如果译成“我吸烟有三年了”,应为:It is three years since I began to smoke. | 
