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。

一旦开了头，你就应当继续下去。Once you begin, you must continue .

你一旦见过他，就不会忘了他的。Once you see him, you will never forget him .

下次，  next time .

第一次， the first time .

最后一次，the last time .

 每次every time .

下次你进城一定来看我们。be sure to call on us next time you come to town .

我第一次见他时，他给我留下了好印象。He left me a good impression the first time I met him .

我每次见到他，他都是一付痛苦的表情。Every time I see him he looks miserable .

上一次我和他谈话时，他看上去很开心。The last time I spoke to Bob, he seemed happy enough .

by the time 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。

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 )By the time he was fourteen, Einstein had learned advanced mathematics all by himself .

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 )I shall have finished my work by the time you return .

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。

武汉位于长江和汉水汇合处。Wuhan lies where the Yangtze and the Han River meet .

有志者，事竟成。Where there is a will, there is a way .

我的书在我原来放的地方找到了。I found my books where I had left them .

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 )You'd better make a mark where you have any questions .

注意：在地点状语从句之前，不要使用介词。

你应该把书放在原来的地方。 You should put the book where it was .

我们应该到最需要我们的地方去。 We should go where we are needed most .

 在任何地方，无论哪里Wherever.

不论到什么地方，都要把工作做好。Wherever you go， you should do your work well .

你爱坐哪儿就坐哪儿。You may sit down wherever you like .

他们每到一处都受到了友好的接待。Everywhere they went， they were kindly received .

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 ，因为， because， 因为，since，由于 now that ，既然, considering that，就，而论, seeing that ,鉴于。

因为我喜欢，所以我才干。Because I like it, I do it .

他不可能见过我，因为当时我不在那儿。He couldn't have seen me, because I was not there .

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。

由于他不遵守规章制度，他受到了处罚。 Because he did not obey the rules,he was punished .

for 表示的是推断解释，

because 强调动作发生的直接原因。

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）it must have rained last night, for the ground is wet .

天亮了，因为鸟在叫。（不可用 because，因为鸟叫不是天亮的原因）The day breaks, for the birds are singing .

由于他累了，所以他很早就上了床。（直接的理由）He went to bed early, because he was tired.

他肯定累了，因为他很早就上了床。（间接的推断）He must be tired,  for he went to bed early .

在强调结构 it is + that 和it was +that 和关联词 not+ but 引导的原因状语从句中，宜用 because 。

正是因为他帮助过你，所以我乐意去帮助他。it 's because he helped you that I'm prepared to help him .

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。He decided to give up the chance of going abroad， not because he did not want to, but because his wife was ill .

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。

因为你没有驾驶执照，所以不允许你开车。Since you have no licence, you are not allowed to drive .

既然大家都来了，咱们就设法做出一个决定吧。Since you are all here, let's try and reach a decision .

as 由于。一般多用于句首。

由于病了，她没来参加晚会。as she was ill, she didn't come to the party .

由于他身体欠佳，我只好不带他去了。as he was not well enough, I had to go without him .

由于下雨我们都呆在家里。as it rained,  we all stayed at home .