1．when ①when表示点时间时，从句中用短暂性动词；表示段时间时，用持续性动词。 When I got home, my family were already having dinner. 我到家的时候，全家已在吃晚饭。 （when表示点时间） When they were still talking and laughing, the teacher came in. 当他们还在说笑的时候，老师进来了。（when表示段时间） He waved ahello when he saw her. 当他看见她的时候，就挥手打了个招呼。（when表示点时间） When you think you know nothing, you begin to know something. 当你认为自己一无所知的时候，就开始知道一些事情了。（when表示段时间）
注意： 当when意思是正当……时候（and at that moment）时，when只能跟在前一分句之后。 He was about to go to bed when the doorbel rang. 他正要上床，忽然门铃响了。 They were watching the World Cup when suddenly the lights went out. 他们正看着世界杯比赛，突然灯灭了。 They had just arrived home when it began to rain. 他们刚到家，天就开始下雨了。 ②有时when表示虽然，尽管的含义，相当于although或since。 He walks when he might take a taxi. 尽管可以打的，但他还是步行。 How can you hope for mercy yourself when you show none 既然你不宽恕别人，你自己又怎能希望得到别人的宽恕呢？
2．while ①while通常表示一段时间，从句中宜用持续性动词作谓语。 Strike while the iron is hot. 趁热打铁。 She fell asleep while she was reading the newspaper. 她在看报的时候睡着了。 ②while有时可以作并列连词，表示对比，可译成……而……。 I am fond of English while he likes maths. 我喜欢英语而他却喜欢数学。 We slept while the captain kept watch. 我们睡觉而上尉担任警戒。 ③while有时可引导让步状语从句，意思是虽然。 While they love te children, they are strict with them. 虽然他们都爱他们的孩子，但却对他们要求严格。 提示： 虽然during 与 while 意思很相近，但是during是介词，不能引导从句。
3．as ①as表示点时间时，从句中用短暂性动词；表示段时间时，用持续性动词。as和when两者经常可以通用。 The thief was caught as when he was stealing in the supermarket. 小偷在超市行窃时被逮住了。 I saw Jim as when he left the meeting room. 吉姆离开会议室时候我看到了他。 ②as表示 一边……一边……，强调从句和主句中两个动作交替进行或同步进行。 They talked as they walked. 他们边走边聊。 He looked behind from time to time as he went. 他一边走，一边不时地往后看。 ③as表示随着 As time goes on, it's getting warmer and warmer. 随着时间的推移，天气变得越来越暖了。 As spring warms the earth, al flowers begin to bloom. 随着春回大地，百花开始绽放。
4．when, while, as的用法区别 ①只有当从句表示的是段时间，即其谓语动词有持续性特征时，这三者可以通用互换。 I got the news on the radio when while as I was having breakfast. 我在吃早饭的时候从收音机里获悉这一消息。 ②在下列情况下，三者彼此之间不能替换使用： a．as更强调同一时间或紧接的一前一后或伴随着的变化。 We listened to the singer sing as he played the guitar. 我们听着歌星边弹吉它边演唱。 I thought of it just as you opened your mouth. 你一张嘴我就知道你要说什幺 As he grew older, he became less and less active. 随着他年龄的增长，他变得越来越不活泼了。
提示： 状语从句可放在主句之前或之后，放在主句之前时一般用逗号与主句分开。有时可置于主句中间，前后用逗号。 b．when更强调特定时间，还可表示从句中的动作先于或后于主句的动作。 When I had given Mary the spare ticket, I found my own already gone. 当我把多余的票给了玛丽时，我才发现我自己的票已不知去向。（从句动作发生在主句之前，注意主从句的时态） When I finally got there, he meeting had been on for ten minutes. 当我最终赶到那里时，会议已开始十分钟了。（从句动作发生在主句之后，注意时态） c．while从句只能表示延续的动作或状态或主从句中动作的对比。 She thought I was talking about her daughter, while in fact, I was talking about my daughter. 她以为我在谈论她女儿，而事实上，我在谈论我的女儿。 d．若表示两个短促动作几乎同时发生时，用as场合多于when。 As he finished his speech, the audience burst into applause. 他结束讲话时，观众爆发出雷鸣般的掌声。
5．whenever whenever是when的强势语，它描述的不是一次性动作，而是经常发生的习惯性动作。 You are always welcome whenever you come. 无论你何时来都欢迎。 Whenever we met with diffiulties, they came to help us. 每当我们遇上困难的时候，他们就来帮我们。
B． before, after
1．before before表示在一段时间之前。 I must finish all the work before go home. 回家之前我必须干完所有的活。 You must first learn to walk before you try to run. 在想要跑以前，你得先学会走。 He had learned English for three years before he went to London. 他去伦敦之前已学了三年英语。 提示： before 从句往往带有否定的含义。 He ran off before I could stop him. 我还没来得及阻止他，他就跑掉了。 Thke it down berore you forget it. 趁着还没忘记的时候就记录下来。 必背： before 常用句型 It is was will be �before� It wil be five years before we meet again. 五年以后我们才能再见。 It will be not long before you regret what you have done. 不用过多久你就会对你所作所为感到后悔的。 It was not long before I realized I was wrong. 不久我就意识到我错了。 It was minutes before the police arrived. 过了几分钟警察才到。
2．after after表在一段时间之后。 Let's play football after school is over. 放学后我们踢足球吧。 The sun came out soon after the storm stopped. 暴风雨过后不久，太阳出来了。
C．till, until 1．untiltill用于肯定句时，表示直到 为止，主句必须为持续性动词。 We shall wait until till he comes back. 我们将一直等到他回来。 (注意它们的拼写) Everthing went well untiltill that accident happened. 直到发生那意外之前，一切都正常。 2． not�untiltill表示直到 才 ，主句通常要用短暂动词，这时until和till可用before代替。 I didn't leave until till before she came back. 直到她回来，我才离开的。 Bells don't ring till until you strike them. 铃不打不响。 Peopl do not know the value of their health till until before they lose it. 人们直至失去了健康才知其可贵。 3．当not until位于句首时，主句中的主语、谓语要使用倒装语序。 Not until she stopped crying did I leave. 直到她不哭了，我才离开的。
注意： until引导的从句可以放在主句之前或主句之后，但till从句一般不放在句首。 4．在强调句型中一般只能用until，不用till。 It was not until she took off her drk glasses that I recognized her. 直到她摘下墨镜，我才认出她。
D．since, ever since 1．since自……以来。表示动作从过去某一点时间一直延续到说话时间为止。主句中通常为延续性动词的现在完成时，since从句中一般用短暂性动词的一般过去时。 It has been just a week since we arrived here. 我们到这儿刚刚一星期。 Where haveyou been since I last saw you 自上次我见过你之后，你去了哪里？ Since she was young, she has been collecting stamps. 她自年轻时起就一直集邮至今。
提示： 有时since 从句中也可以用延续性动词，注意它的译法。 Tom is now working on the farm.It's two years since he was a college student. 汤姆现在农场上班，他大学毕业已有两年了。 2．ever since 从那时起直至现在，此后一直。表示说话者强调主句动作或状态持续时间长，语气比since强。 Ever since they got married in 1950, they have lived happily. 自一九五零年结婚以来，他们一直生得很幸福。
3．since还可以用作副词或介词。 The big clock was damaged during the war and has been sient（ever）since. 这只大钟在战争中损坏了，从此就一直不响了。 My uncle went to Tibet in the 1950s. He has been living there（ever）since. 我叔叔五十年代就去了西藏，从那以后他一直生活在那里。 You have made great achievements in your work since graduation. 你们自毕业以来已经在工作中取得了巨大成就。
E．as soon as as soon as...可译为一……就……，用来表示主从句的动作是紧接着发生的。 He will come and see you as soon as he can. 他一有空就来看你。 He rushed home as soon as he got the good news. 他一得到这个好消息就奔回家。 必背： 一……就……还可以用onupon doing 结构来表示。 On arriving home he called up Lester. = As soon as he arrived home, he called up Lester. 他一到家就给莱斯特打电话。
F． immediately instantly directly 相当于as soon as，从句中用一般过去时态。 They phoned her immediately they reached home. 他一到家马上就给她打了电话。 I recognized her instantly I caught a glimpse of her. 我一看见她就把她认出来了。 We came directly we got your telephone. 我们一接到你的电话就赶来了。
G．the moment, the minute, the instant, the second 这几个名词短语也可用作连词，直接引导时间状语从句，表示一 就 。 He said he'd turn on TV th moment he got home. 他说他一到家就打开电视机。 Tell him I need to see him the minute he arrives. 告诉他，他一到我就要见他。 The second the bell rang, the students rushed out of the classroom. 铃一响，学生就冲出了教室。
H．hardly scarcely�when�, no sooner�than� 这两个短语都表示刚……就……，可以互换，主句通常用去完成时。 He had no sooner started out than he felt homesick. 他刚出发就想起家来。 He had hardly started his speech when someone rose to refute his points. 他刚开始发言，就有人站起来反驳他的论点。 注意： 当hardly, scarcely, no sooner 位于句子的开头时，主句须用倒装语序。 Hardly had she fallen asleep when a knockat the door woke her up. 她刚要睡着，忽然敲门声把她吵醒。 No sooner was the frost off the ground than the work began. 地上的霜一消散，人们就开始工作了。
I．once once作连词时，也相当于as soon as，但它含有的条件意味更浓，它引导的从句较短。 Once you begin, you must continue. 一旦开了头，你就应当继续下去。 Once you see him, you will neer forget him. 你一旦见过他，就不会忘了他的。
J．next time, the first time, the last time, every time 等 Be sure to call on us next time you come to town. 下次你进城一定来看我们。 He left me a good impression the first time I met him. 我第一次见他时，他给我留下了好印象。 Every time I see him he looks miserable. 我每次见到他，他都是一付痛苦的表情。 The last time I spoke to Bob, he seemed happy enough. 上一次我见到他时，他看上去很开心。 K．by the time by the tine 也可以引导时间状语从句，意为到 时为止，主句一般要用完成时态。 By the time he was fourteen, Einstein had learned advanced mathematics all byhimself. 爱因斯坦到十四岁时就自学完了高等数学。 (从句为一般过去时，主句要用过去完成时) I shall have finished my work by the time you return. 在你回来之前我将会做完我的活儿。(从句为一般现在时，主句要用将来完成时)
