职称英语考试：重点语法精讲
状语从句指句子用作状语时，起副词作用的句子。它可以修饰谓语、非谓语动词、定语、状语或整个句子。
根据其作用可分为时间、地点、原因、条件、目的、结果、让步、方式和比较等从句。状语从句一般由连词（从属连词）引导，也可以由词组引起。从句位于句首或句中时通常用逗号与主句隔开，位于句尾时可以不用逗号隔开。
【考点聚焦】
时间状语从句
(1)as、when、while
as表示“当……的时候”，往往和when/while通用，但它着重强调主句与从句的动作或事情同时或几乎同时发生。
She came up as I was cooking.（同时）
The runners started as the gun went off.（几乎同时）
when：（at or during the time that）既可以表示在某一点的时候，又可表示在某一段时间内，主句与从句的动作或事情可以同时发生也可以先后发生。
It was raining when we arrived.（指时间点）
When we were at school, we went to the library every day.（在一段时间内）
while意思是“当……的时候”或“在某一段时间里”。主句中的动作或事情在从句中的动作或事情的进展过程中发生，从句中的动词一般要用延续性动词。在when表示a period of time时，两者可以互换。
Please don't talk so loud while others are working.
He fell asleep while/when reading. Strike while the iron is hot.（用as或when不可，这里的while意思是“趁……”）
(2)引导时间状语从句的连接词除上述外还有：
①till、not…until…、until、before、since
Don't get off the bus until it has stopped.
He waited for his father until(till)it was twelve o'clock.
It will be five years before he returns from England.
让步状语从句
(1)although与though可以引导让步状语从句，不能与but连用，但可以与yet连用。
Although they are poor,(yet)they are warm-hearted.
(2)even if或even though引导让步状语从句，表示“即使”，"“纵然”，用来使人注意下文所强调内容的性质。
I'll get there even if(though)I have to sell my house to get enough money to go by air.
(3)no matter后接上who、what、where、how等疑问词，也可以在这类疑问词后面加上ever构成whoever、whatever、wherever、however等。
Don't trust him, no matter what / whatever he says.
Whoever breaks the law will be published.
No matter how hard the work is, you'd better try to do it well.
(4)as也可以引导让步状语从句，要用倒装。
Child as(though)he is, he knows a lot.
Much as I like it, I won't buy.
Try as he would, he couldn't lift the heavy box.
