职称英语重点语法解析之让步状语及时间状语
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。
让步状语从句
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,they are warm-hearted.
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。
Ill get there even ifI have to sell my house to get enough money to go by air.
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。
Dont trust him, no matter what / whatever he says.
Whoever breaks the law will be published.
No matter how hard the work is, youd better try to do it well.
as也可以引导让步状语从句，要用倒装。
Child ashe is, he knows a lot.
Much as I like it, I wont buy.
Try as he would, he couldnt lift the heavy box.
时间状语从句
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.
The runners started as the gun went off.
when：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.
When we were at school, we went to the library every day.
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 dont talk so loud while others are working.
He fell asleep while/when reading. Strike while the iron is hot.
引导时间状语从句的连接词除上述外还有：
①till、notuntil、until、before、since
Dont get off the bus until it has stopped.
He waited for his father untilit was twelve oclock.
It will be five years before he returns from England.