1．时间状语从句
1）when, as, while
a)when表示“当…时”。when引出的时间状语从句，其中的动词既可以是延续性动作的动词，也可以是瞬间性动作动词。可以表示主句的动作和从句的动作同时发生，或者从句的动作发生在主句的动作之前。
如：When you apply for a job, you must present your credentials.当你申请工作时，你必须递交你的有关证件。（同时）
When the students heard the teacher’s footsteps, they all stopped talking. 当学生们听到老师的脚步声时，他们都停止了说话。（从句动作发生在前）
when还可以表示just then（正在那时）的意思，此时其引导的从句只放在主句之后。
如：we were about to start when it began to rain.我们正要动身，突然下起雨来。
b) while表示“在…期间”或“在某一段时间里”，其所引导的从句的动作是延续性的，并侧重表示和主句动作的同时发生。
如：While the teacher paraphrased the text in English, the students listened attentively and took notes.当老师用英语阐释课文时，同学们注意地听并且做着笔记。
The door bell rang while I was watching TV.我正在看电视的时候门铃响了。
while 还可以做并列连词，相当于whereas,连接一个表示对比的并列分句。
如：Mary was dressed in blue while Jane was dressed in red.玛丽穿蓝色的衣服，而珍妮穿红色的衣服。
c)as 表示“当…时”或“一边…一边”。他引导的时间状语从句的动作也是延续性的，并且侧重主句动作和从句动作的同时发生。
如：As the students walked to their dorms, they sang happily.学生们一边往宿舍走，一边快乐的唱着歌。
2002 年第23小题
___ I knew him better , I discovered that my impression had been right
A which B as C until D unless
答案是B
2）whenever, each time, every time任何时候；每当
如：Whenever/Every time/Each time I met her, she was studying.我每次看见她时，她总是在学习。
3)since(自从)，ever since(从那时起一直到现在)
since, ever since 引导的从句通常用一般过去时，主句中的谓语动词用完成时。
如：We have never met since we graduated from the college.我们自从大学毕业后就没有见过面。
4）before（在……之前），after(在……之后)
before 引导的从句一般表示主句的动作发生在从句动作之前，如从句是过去时，主句一般要用过去完成时。after引导的从句，表示主句的动作发生在从句的动作之后，如主句是过去时，从句一般用过去完成时。
如：I had written my dissertation before my supervisor went abroad.在导师出国之前，我已完成了我的学位论文。
After the boy had finished his homework, he played football with his friends.这个小男孩在完成作业后，和他的小伙伴们踢了一会球。
5) till, until
如果主句的谓语动词是延续性动词，就常用肯定式表示“直到……为止”
如：He will remain in college until (till) he finished his Ph.D course.他将留在学校里面直到完成他的博士学位课程。
如果主句的谓语动词是瞬间动词，就常用否定表示“直到……才”
如：I will not go with you until ( till) I finish my homework.等我做完作业我才和你一起去。
6) as soon as, immediately, directly, once, the moment, no sooner…than, hardly…when等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了。即“一……就”。
如：As soon as we got home, the telephone rang.我们一到家，电话就响了。
注：no sooner…than, hardly…when引导的从句，主句中的动词用过去完成时，从句用过去时。且no sooner, hardly位于句首，要倒装主句的主谓。
He had no sooner arrived home than he was asked to start on another journey.他一到家，就又要出另一次差。
No sooner had he arrived home than he was asked to start on another jouney.
2003年25小题
No sooner had he sat down to lunch ___there was a knock at the door .
A when B that C as D than
答案是D
2.地点状语从句
引导地点状语从句的连词有：where (在……地方)， wherever (无论哪里)，everywhere (到处)， anywhere (任何地方)等。
如：Where there is a will, there is a way. 有志者事竟成。
You can go wherever you like these days.这些天你可以去你想去的地方。
3．原因状语从句
1）because表示人们不知道的直接的原因或理由，着重点在从句，即because引出的从句为全句句意的中心所在。通常用于回答why提出的疑问，语气最强，除了特别强调外，该从句一般位于主句后面。
since表示对方已知的、无须加以说明的既成事实的理由。全句的中心在主句上，语气比because弱，译为“既然”。引出的状语从句一般放在句首。
as表示十分明显的原因，一般说明因果关系，着重点在主句，语气更弱，常译为“由于”。引出的状语从句一般放在句首。
for 引出的分句，语气最弱，主要是补充说明原因，解释另外一个分句，且只能放在句子后部。
如：I didn’t go abroad with her because I couldn’t afford it.我没有和她一起出国是因为费用太高。
Since traveling by air is much faster, they decided to take a plane.既然乘飞机旅行快得多，他们就决定坐飞机。
As it is snowing, we shall not climb the mountain.由于在下雪，我们就不爬山了。
It must have rained last night, for the ground is wet.昨晚准下雨了，地面是湿的。
2）now that, seeing that, considering that, in that表示鉴于，由于。in that只能放在主句之后。
如：Now that you have passed your test, you can drive on your own.你驾驶考试既然已经合格，就可以独自开车了。
Seeing that the weather is bad, we’ll stay at home.由于天气不好，我们要呆在家了。
I am in a slightly awkward position, in that he’s not arriving until 10th.我的处境有点难堪，因为他要十号才来。
