3.由till或until引导的时间状语从句。

　　till和until一般情况下两者可以互换，但是在强调句型中多用until。并且要注意的是：如果主句中的谓语动词是瞬时动词时，必须用否定形式；如果主句中的谓语动词是延续性动词时，用肯定或否定形式都可以，但表达的意思不同。例如：

　　I didn't go to bed until(till) my father came back。直到我父亲回来我才上床睡觉。

　　It was not until the meeting was over that he began to teach me English。直到散会之后他才开始教我英语。

　　I worked until he came back。我工作到他回来为止。

　　I didn't work until he came back。他回来我这才开始工作。

　　Please wait until I arrived。在我到达之前请等我。

　　4.由since引导的时间状语从句。

　　since引导的从句的谓语动词可以是延续性的动词，又可以是瞬时动词。一般情况下，从句谓语动词用一般过去时，而主句的谓语动词用现在完成时。但在It is ＋时间＋since从句的句型中，主句多用一般现在时。例如：

　　I have been in Beijing since you left. 自从你离开以来，我一直在北京了。

　　Where have you been since I last saw you? 自上次我和你见面以后，你到哪里去了？

　　It is four years since my sister lived in Beijing. 我妹妹不在北京住有四年了。

　　It is five months since our boss was in Beijing。我们老板离开北京有五个月了。

　　知识扩展

　　1. It is since从。。。以来多长时间了(因为since +从句或名词，表示一段时间)

　　It is five years since we met last time。从我们上次见面已经五年了。

　　2. It is +before…(。。。才)

　　It was a long time before I went to sleep again。

　　过了很长时间我才睡着。

　　It was an hour before(＝until) the police arrived。

　　过了一个小时，警察才来。

　　5.由as soon as, immediately, directly, instantly, the moment, the instant, the minute, 等引导的时间状语从句。这些连词都表示“一……就”。例如：

　　I will go there directly I have finished my breakfast. 吃完早饭，我立即到那里去。

　　The moment I heard the news, I hastened to the spot。我一听到消息，马上赶到了出事地点。

　　As soon as I reach Canada, I will ring you up. 我一到加拿大，就给你来电话。

　　【注意】hardly(scarcely, rarely)…when / before, no sooner…than相当于as soon as之意。主句用过去完成时，从句用一般过去时。当hardly, scarcely, rarely和no sooner位于句首时，主句应用倒装语序。例如：

　　He had no sooner arrived home than he was asked to start on another journey. 他刚到家，就被邀请开始另一旅程。

　　No sooner had the sun shown itself above the horizon than he got out of bed to commence work。太阳刚从地平线上升起，他就起床劳动去了。

　　Hardly had I sat down when he stepped in。我刚坐下，他就进来了。

　　He had hardly fallen asleep when he felt a soft touch on his shoulder。这个阿拉伯人刚要入睡就感到肩膀上被轻轻一触。

　　6.由by the time引导的时间状语从句。

　　注意时态的变化：在一般情况下，如果从句的谓语动词用一般过去时，主句的谓语动词用过去完成时；如果主句的谓语动词用一般现在时，主句的谓语动词用将来完成时。例如：

　　By the time you came back, I had finished this book。到你回来时，我已经写完这本书了。

　　By the time you come here tomorrow, I will have finished this work. 你明天来这儿的时候，我将已经完成此工作了。

　　7.由each time, every time和whenever引导的时间状语从句。例如：

　　Each time he came to Harbin, he would call on me. 他每次来哈尔滨，总是来看我。

　　Whenever that man says“To tell the truth”， I suspect that he's about to tell a lie。每当那个人说“说实在话”的时候，我猜想他就要说谎了。

　　You grow younger every time I see you. 每次遇到你，见你更年轻了。

　　8.由as long as和so long as引导的时间状语从句。这两个连词表示“有多久……就多久”。例如：

　　You can go where you like as long as you get back before dark. 你可以随意到哪里去，只要在天黑以前回来就行。

　　I will fight against these conditions as long as there is a breath in my body! 只要我一息尚存，我就要反对这种境况。