3．在强调结构It is/was…that和关联词not…but 引导的原因状语从句中，宜用because。
It's because he helped you that I'm prepared to help him.
正是因为他帮助过你，所以我乐意去帮助他。
He decided to give up the chance of going abroad, not because he did not want
to but because his wife was ill.
他决定放弃出国的机会，不是因为他不想去，而是因为他妻子病了。
B． since
since 因为，既然。引导的从句大多置于句首，主从句的时态一般相同。
Since you have no license, you are not allowed to drive.
因为你没有驾驶执照，所以不允许你开车。
Since you are al here, let's try and reach a decision.
既然大家都来了，咱们就设法做出一个决定吧。
C．as
as 由于。一般多用于句首。
As she was ill, she didn't come to the party.
由于病了，她没来参加晚会。
As he was not well enough, I had to go without him.
由于他身体欠佳，我只好不带他去了。
As it rained, we all stayed at home.
由于下雨我们都呆在家里。
C． because, since, as 的区别
2．for 表示的是推断解释，because强调动作发生的直接原因。
It must have rained last night, for the ground is wet.
昨晚肯定下雨了，因为地面是湿的。(不可用because，因为地面湿不是天下雨的原因)
The day breaks, for the birds are singing.
天亮了，因为鸟在叫。(不可用because，因为鸟叫不是天亮的原因)
He went to bed early, because he was tired
由于他累了，所以他很早就上了床。(直接的理由)
He must be tired, for he went to bed early.
他肯定累了，因为他很早就上了床。(间接的推断)
原因状语从句是表示原因和理由的从句。引导原因状语从句的有as, because, since, now (that), considering that, seeing that等。
A．because
because因为
Because I like it, I do it.
因为我喜欢，所以我才干。
He couldn't have seen me, because I was not there.
他不可能见过我，因为当时我不在那儿。
比较：
because 和for的区别。
1．for 是并列连词，只用于连接表示原因的分句，因此不能用于句首。because表示原因时，可位于句首。
[误]For he did not obey the rules, he was punished.
[正]Because he did not obey the rules, he was punished.
由于他不遵守规章制度，他受到了处。
地点状语从句通常由where, wherever(where的强势语)和everywhere引导，是表示空间关系的状语从句。
A． where
where 在……地方，去……地方
Wuhan lies here the Yangtze and the Han River meet.
武汉位于长江和汉水汇合处。
Where there is a will, there is a way.
有志者，事竟成。
I found my books where I had left them.
我的书在我原来放的地方找到了。
You'd better make a mark where you have any questions.
哪儿有问题，你最好在哪儿做个记号。(这里where引导的从句不是定语从句)
注意：
在地点状语从句之前，不要使用介词。
[误]You should put the book at where it was.
[正]You should put the book where it was.
你应该把书放在原来的地方。
[误]We should go to where we are needed most.
[正]We should go where we are needed most.
我们应该到最需要我们的地方去。
B. wherever
wherever在任何……地方，无论哪里
Wherever you go, you should do your work well.
不论到什么地方，都要把工作做好。
You may sit down wherever you like.
你爱坐哪儿就坐哪儿。
C. everywhere
Everywhere they went, they were kindly received.
他们每到一处都受到了友好的接待。
3．since还可以用作副词或介词。
The big clock was damaged during the war and has been silent(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on/upon 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 the 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。
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 knock at 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 never 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 by himself.
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)
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。
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 have you 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。
4．在强调句型中一般只能用until，不用till。
It was not until she took off her dark glasses that I recognized her.
直到她摘下墨镜，我才认出她。
D．since, ever since
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。
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。
2． Not until/till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。
People 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。