引导状语从句的几组特殊的词精析精练
1. while, when, as
（1）as, when 引导短暂性动作的动词。 
Just as / Just when / When I stopped my car, a man came up to me. 
当我把车停下来，意为男士走过来。
（2）当从句的动作发生于主句动作之前，只能用when 引导这个从句，不可用as 或 while。
When you have finished your work, you may have a rest. 
当你完成了自己的工作，你可以休息一下。
（3）从句表示"随时间推移"连词能用as，不用when 或while。
As the day went on, the weather got worse.

日子一天天过去，天气越变越坏。

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2. until和till
此两个连词意义相同。肯定形式表示的意思是"做某事直至某时"，动词必须是延续性的。否定形式表达的意思是"直至某时才做某事"。动词为延续性或非延续性都可以。正确使用这两个连词的关键之一就在于判断句中的动词该用肯定式还是否定式。
（1）肯定句 
I slept until midnight. 我一直睡到半夜时醒了。
注意：在肯定句中可用before代替，如：Let's get in the wheat before the sun sets. 
（2）否定句 
I didn't manage to do it until you had explained how. 直到你教我后，我才会做。 
（3）Until可用于句首，而till通常不用于句首。 
Until you told me, I had heard nothing of what happened. 
直到你告诉我以前，出了什么事我一点也不知道。
（4）Until when 疑问句中，until要放在句首。 
---Until when are you staying? 你呆到什么时候？--- Until next Monday. 呆到下周一。
注意： Not until …在句首，主句用倒装。 例如：
Not until the early years of the 19th century did man know what heat is.
直到19 世纪初，人类才知道热能是什么。 

1.He had come to the right place at the very beginning but failed to find the bone ________ he only complained and didn't try at all.
2.—Can I lie about seeing a text because I was too busy or lazy to respond to it?
—Receiving a text does not necessarily mean you have to respond. Why waste a perfectly good lie _____the truth will serve?
3.________ I booked the ticket, you promised to drive non－stop from Aye to Norwich.
4.________ life in a new country can be difficult，it can broaden a person's view of the world.
5.________ the bees do not learn which smells mean food，they will starve.
【答案与解析】
1. because
【解析】分析句意可知，空后是前面的分句的原因，故填because。
4. While/Although/Though 
【解析】句意：尽管在一个新的国家生活是很困难的，但是它可以开阔眼界。根据句意，前后之间为让步关系，所填词引导让步状语从句，故填While/Although/Though。
5. If 
【解析】句意：如果蜜蜂不能闻出食物的味道，它们会饿死。根据句意可知此处要用if来引导条件状语从句。

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